In praise of insets

Sky News reports on the Scottish politician Tavish Scott (real name) as he proposes a ban on maps that use an inset to show Shetland. Utter nonsense.

His reasoning is that the 'islands should be in the right place on the map' and 'to ensure that in future that government publications and documents do reflect the reality of Scotland in terms of its geography, and not something that fits neatly on an A4 sheet of paper.'

Well let's just break down (sorry, I mean utterly destroy) his preposterous statements. Shetland (The Shetland Isles) is a part of Scotland. It's also part of Great Britain...and the British Isles... and the United Kingdom (and at the time of writing at least, Europe). The following usefully clarifies the terminology:

So in that sense it has a rightful place on any map of which any of those jurisdictions is the focus.

If you're not aware of where Shetland is in the world then this should help (map to scale, UK National Grid):

In simple geographical terms Shetland is approximately 130 miles from mainland Scotland though it's also on the same line of latitude as Bergen on the west coast of Norway at a distance of 200 miles. That's where it sits. At a nice northerly 60° 9' 11" N and 1° 8' 58" W. We can argue all you like whether it should be part of Scotland or, perhaps, a bit of waste left over from Slartibartfast's design of the Norwegian coastline but for now, it gets put on maps of Scotland and any other that includes Scotland. And that makes it a pain in the arse for cartographers.

By the way, did anyone spot I deleted France from the map above? Guess that'd annoy the French too but whatever, I doubt the scots or Scott cares much about that little cartographic editorial decision.

Anyway, as the scot, Scott, says, many maps are made on A4 (or any A series piece of paper where the length and width are in the same proportion). So here's the above map proportioned as A4:

The area outside the yellow line is superfluous to the map as the Republic of Ireland is irrelevant on many maps that show thematic data for Great Britain and Northern Ireland (or UK etc). So as a rough estimate the page only uses approximately 60% of its overall space to show the mapped content.

Put another way, we need a fifth of the entire page (above the green line) just to get Shetland on. That's Shetland, population 22,000. Or, in geographical terms, an island that is 566 sq miles which is 8x larger than the City of Glasgow but which has 27x fewer people. So you're making a decision to allow geography to not only influence the design but take an inordinately exaggerated status simply by virtue of position.

Now, admittedly there's lots of lovely space for titles and legends and all the other crap we put on a map but, nevertheless, it's wasteful. But that's what you'd have to do if you want Shetland on the map, on that proportion of paper, in its correct geographical position. Alternatively, as Scott bemoans, cartographers will often use an inset and you'd end up with a map like this:

This fits the map to the paper (not the paper to the map). And there's far less wasteful space. Far less prominence to unpopulated swathes of water. And yet Shetland gets its own little special place on the map, with the addition of a neat border that clearly demarcates it. Often, Shetland is even exaggerated in scale to make the inset worthwhile. I bet you didn't notice but in the example above Shetland is about 25% bigger than it really is. So, if Scott wants Shetland back in its proper geographical location then he can have it reduced back to its real size too.

Insets are a neat solution and one that has served print mapping well for centuries. It's also a solution that people understand. You could add a small arrow and distance marker to point to where the inset exists in reality. Many even use a marked graticule to show clearly the lines of latitude and longitude that apply to the inset to make it clear that it differs from that of the main map. Even the Sky News article showed an historical example that clearly uses this technique (and note how exaggerated in size Shetland is on this too):

There's other considerations...

Returning to the City of Glasgow. In fact, any relatively populous place. They suffer horrendously on any maps of thematic data because large areas, perhaps relatively uninhabited or sparsely populated take visual prominence. Scotland is a great example. Its total population is around 5.3 million yet 1 million of them live in Glasgow and Edinburgh. Their population densities are far more than the far greater share of Scottish land, including Shetland. So why give such visual prominence to sparsely populated areas?

Insets are not just used to move geographically awkward places. They are commonly used to create larger scale versions of the map for smaller, yet more densely populated places. Often they are positioned over sparsely populated land to use space wisely. I'm guessing Scott would have an objection to an inset that, to his mind, would exaggerate the geographical importance of Glasgow compared to Shetland. Yet...in population terms it's a place of massively greater importance so one could argue it deserves greater relative visual prominence on the map. Many maps are about people, not geography.

In addition to moving Shetland south to make better use of map space, you could very well argue that you should use a cartogram to give far better relative visual prominence to the places where more people live and work. Now that will utterly delight Scott as it completely distorts geography. Not only could you have Shetland moved, but squished to an almost unrecognisable shape. Here you go Tavish...enjoy this beauty of population totals morphing geography (courtesy: worldmapper.org):

Whatever your view of insets (and Scott's is incorrect), there's so many valuable uses for them that counter the problems of geography making it awkward to make maps. Generations of cartographers have come up with novel solutions to many, if not all, of these dilemmas about what to show, where and how. And if the map has an overarching location map showing everything in its correct position then there can be absolutely no confusion whatsoever.

I would guess Scott would equally be horrified if Shetland was seen poking outside the graticule or neatline on an atlas page too - another common way in which maps break the rules of either geography or design in a creative way to simplify and communicate. He'd be delighted by this classic Times Atlas of the World page showing Shetland in its correct position as part of The British Isles but horrors of horrors...Rockall (also a part of Scotland so has equal rights on a map based on Scott's nonsense...but ignore the more northerly Faroe Islands, not part of Scotland) slips off the left edge:

And what of digital maps? Scott seems to be stuck in the age of print cartography because insets are rarely, if ever, a requirement in digital cartography. Everywhere exists where it is. The map is slippy and you can pan and zoom to your heart's content. Want to see a densely populated area? Zoom right on in. In fact, whisper it quietly in case Scott is listening but...if he uses the standard Web Mercator web map he not only gets Shetland in its rightful position AND it's also exaggerated in size compared to the southerly latitudes of mainland England by virtue of the projection. Now isn't that the map he really wants?

Update  4th October 2018

As BBC News reports Mr Scott has got his way and a bill has been passed that includes a 'mapping requirement' that Shetland not be placed in a box. Fortunately there's a clause allowing cartographers to use an inset if they have a case to do so...so that's OK then because there's always a case to do so UNLESS you're making a navigational chart where distance, direction and bearings are obviously the paramount need for the map's properties and design to support. But all this really means is time wasted and taxes used up as map-makers submit their case to use an inset for Shetland.

So, where do we go from here? If Alaska and Hawaii find out about this nonsense then it's going to make future US maps rather interesting. And please don't get the Falkland Islands worked up and starting to assert their right to be included on maps of the UK. As a British Overseas Territory, they, along with the rest, may very well start insisting they should be on the map, in the correct location. So, here's your updated map Mr Scott. Shetland is in the right place but you can't see it any more because we've had to include all the British Overseas Terretories as well. Sorry about that but they all have an equal right. I do hope you appreciate it's a useless map for showing important geographies of the UK though. That's what the new 'mapping requirement' law promotes - bloody ridiculous mapping.

Keep the user in mind

I nearly splurged my Corn Flakes all over the breakfast table this morning as I saw various people begin lauding the merits of a new map tool called 'cartogram'. As an avid fan of most forms of cartogram I was immediately interested. Cartograms are hard to make...hard to make well. Was there a new tool to help?

Imagine my surprise when I launched the tool to find it has absolutely sweet FA to do with cartograms. You take a picture, or use one and the map gets 'styled' according to colours in the picture.

Cartogram?

That word cartogram already has a meaning - a map on which statistical information is shown in diagrammatic form That surely couldn't have been too hard to find?  Except Mapbox have re-appropriated the noun as a product that allows you to 'make a map style by dropping an image on the map'.

It doesn't even do that. Style is so much more than just getting an algorithm to take colours from an image and then re-colour basic elements of the map. It allows you to re-colour land, buildings, water, roads and labels. Look, here's a Mona Lisa map style I made:

And this is what happened when I tried to style my map like Google's map:

But my point about it not really being a styling tool is evident when you do want to have some control. This is as close as I could get to Google's Map...and it isn't very close.

Here's my final effort before I got bored...look, it's the Ron Jeremy map:

I'm sure others can be more inventive....

Like I said, style is so much more than basic colouring in by numbers. It's about working with consistent denotation, about placement and typographic control. It's about careful generalization - selection, omission, simplification etc. It's about composition and the human act of making choices to reflect a particular look and feel; a certain aesthetic that ties in with the map's purpose and your desires for the map.

Look, don't get me wrong. It's fun. It's click bait to get you to want to save your map and sign up. I get it. But why can't the thing have a different name. Something that neither sullies a word already in very clear mainstream cartographic use AND something that actually says what the thing does. This isn't the first time there's been a lack of invention in cartographic circles. It wasn't long ago that we saw an entire company decide to truncate its name to an abbreviated form of the word cartography itself. We use the term carto every day, but not to refer to a company.

For my money it's just lazy. It's a lazy choice of name and it's mistakenly suggesting this is what map styling is all about. Come up with a decent name and sell what it is, not what you think you can get away with by corrupting a term that already exists and is well understood. Think of something original. Don't constantly look to take something and try and turn it into some sort of game.

As cartographers are always told, you need to keep the user in mind. With more and more of this sort of bastardization of nomenclature all we do as an industry is confuse the hell out of people.

Just to avoid confusion, here's the entry on cartograms for my forthcoming book. I am not going to change it but I'd recommend it as reading for those who just killed a little piece of cartography with their poor choice of marketing BS. By the way, the book is called Cartography. Because that's what it's about. I also wrote the entry on cartograms for the forthcoming v2.0 of the GIS&T Body of Knowledge. I'm not changing that either.

Grid-O-gram

I had the pleasure of working with Mamata Akella when I first started at Esri. Mamata went on to work for the National Park Service and is now at CartoDB where she seems able to flex her design wings with thematics. This is fertile space in mapping in general and it seems never a week goes by without someone re-inventing a thematic mapping technique, occasionally with a new twist. Mamata's latest map caught my attention.

In response to her call for comments I hope she won't mind me using this blog as a space in which to offer my opinion and insight so here's a critique of the map above.

It's visually arresting. It's one of those maps you immediately stop and look at so it does a great job of getting people to pause and spend some time with it. That's probably the point so it's already done it's job. Because it lacks a title or any popups or marginalia one quickly gets lost though. As Mamata explains, it's a test and, no doubt, not designed to be used as a fully fleshed out project but it would be useful to include the basics.

It's the 2012 US election data. A well worn dataset that's just about exhausted most techniques. I spent some time with it myself a couple of years ago creating a gallery of various thematic map types. But with the 2016 election on the horizon many will be experimenting with new or modified techniques to prepare for that mapping extravaganza (me too...but you'll have to wait for that).

So what's going on in this map? Mamata calls it a 'modified cartogram'. Symbol size is total vote. Colour is the winner (red=republican, blue=democrat). Units are counties.

First off - I like the appearance and I like that it's in an equal area projection (Albers). It's eye-catching and somewhat different. I then quickly get uncomfortable with the function and how the data processing encodes meaning. Clearly the real geographic boundaries have been processed. My sense is a regular grid of rectangles has been used in which to bin the counties that fall within. That explains the regular grid and also the irregular number of symbols per location.

Geographical boundaries have been replaced by an abstract geography. It's referred to as a cartogram, likely because of this abstraction but a cartogram it is not. Cartograms distort space but they don't aggregate in an irregular fashion. Think Gastner-Newman, Dorling, Demers or a basic non-contiguous cartogram which all treat geography in different ways but which do not apply a binning technique as an interim step. Further, cartograms don't have overlaps. Mamata's symbols do overlap. It's therefore difficult to know how many counties are represented by each location and it's difficult to ascertain the distortion of the underlying geography which will inevitably be greater in areas with larger numbers of smaller counties. It's adding in a visual complexity that isn't necessary even though it gives a neat (as in regular - pleasing to the eye) looking final appearance.

I don't particularly like the way transparent overlaps on the symbols yield overlaps with darker shades - to me that visually implies 'more' yet is purely an artifact of symbol size bleeding into an adjacent symbol and not necessarily a function of geography at that place or overlapping geographies. Of course, when we're talking about mixing blues and reds it gets even more difficult to visually disentangle. That''s not a problem simply on this map though. I wrote about it before in regard to proportional symbol maps.

So it's a gridded proportional symbol map? Looks that way. Are symbols stacked? Possibly - in which case a lot of colour is missing due to occluded symbols which changes the ratio of blue:red colour across the map as a whole. If the data is really represented as rings then OK, we're seeing everything but it's also hard to determine why some symbols have more transparency applied than others (strength of vote?).

There's no labels which makes it difficult to describe the pattern verbally and causes even more problems if you don't actually know this is the USA. When you zoom in, the map refreshes with some very big changes in symbol size and larger white spaces so the structure we see for the whole is lost. This makes it hard to retain a mental image of pattern at one scale and compare it to that at another and we very quickly lose where we are on the map.

If it's a proportional symbol map then why not just use geography, even if you discount the boundaries and make a proportional symbol map?

I'll tell you why - they just ain't sexy enough in today's modern mapping landscape. So that's why Mamata experiments. It's why I experiment too. Sometimes we hit, sometimes we miss in our search for something just a little bit unique to develop cartography and showcase the tools and technology of our trade.

For my money this is a miss. I like the look but I think it complicates the subject matter and confuses the cognitive process of understanding the patterns in the data. For me, form should never outperform function. Cartography really is, at its very essence, that art and science of marrying form and function in harmony. You've got to get both right to make a good map.

Back to it being a cartogram - no. It isn't. But maybe Mamata's created a grid-O-gram?

Update: Inevitably, whenever I do one of these critiques I get called out for it being on a map made by someone who works somewhere that I don't. First, Mamata asked for comments. Second, I couldn't care less where she works and this IS NOT about the tech she used. None of my critiques are about the tech. It's about the cartography. Sure, tech affords opportunities or constraints but I don't care one bit about who uses what. This is not about scoring points. I don't publicly critique maps made by colleagues at the place I work because there are better mechanisms for me to use to try and effect change from within. And surely, if anyone thinks it's a good idea openly calling out your employer and those who you work with, you must work in an incredibly forgiving place. I do call co-workers maps out all the time using appropriate avenues. They critique mine too...often in very stark terms. Critique is good. Using different mechanisms to get the job done is important for cartography whomever you work for. So - don't get irate just because Mamata and I work at different companies. It's irrelevant. And yes, many maps I see made by friends, colleagues or whomever are truly awful and I tell them that. Silence in a public space can often be deafening.

Helecxagon mapping

Two things happen whenever there's an election. First, politicians wander round spouting rhetoric in an attempt to persuade us that their colour is the one we should care about. Second, cartographers and map-makers everywhere develop a palpable sense of excitement as a new national dataset is quite literally born overnight. From a cartographic perspective, the recent UK General Election didn't disappoint.

Politically, the Conservative's couldn't have imagined such a result; a majority from seemingly out of nowhere and against all the polls. Labour were trounced and no more so than in Scotland where the Scottish National Party all but turned the map from red to yellow. The UK Independence Party did well in vote share (12.6%) but this translated into only one Parliamentary seat.

For those unfamiliar with how a UK election works, Great Britain and Northern Ireland are subdivided into constituencies. The population of each constituency get to vote for the person (standing on behalf of a political party) they would wish to elect as their Member of Parliament (MP). The votes roll in, are counted, and the person with the most votes wins that constituency 'seat' in Parliament on behalf of their party. There are 650 seats overall and the party that gains a majority of seats gets to form the government as overall winners. So, the party that reaches 326 seats wins. There's a lot of complexities if no single party gets 326 seats but let's not get into that...this isn't a political blog.

So the result was fascinating in and of itself but let's get stuck into the cartography...

Back in 2010 at the last UK General Election most news agencies went with a standard geographic map showing the results by colour of the winning party.

The trouble with this approach is that larger constituencies dominate the map in visual terms. Smaller, inner city constituencies can hardly be seen on a national map like this. It distorts the way we see the election results. On this map there's a lot of blue and a fair bit of yellow and gold. Not much red.

Alternatively, cartograms offer a form of thematic mapping that accommodates the difference in size of areas. There are plenty of alternatives. The Gastner-Newman population density equalizing cartogram tries to preserve some sense of geography while squeezing and stretching shapes. It appears a little odd to some people. The DeMers uses squares, the Dorling uses circles; both perfectly good shapes and then...there's the hexagon. Here's the 2010 results again, this time mapped with equally sized hexagons.

The colours are now equal in terms of the area they occupy on the map. The gold and yellow in the large Scottish constituencies have receded. The blue has also been shifted in visual importance as many far smaller constituencies that elected a Labour MP (red) are now visible. There was a hung parliament in 2010 and the Conservatives (blue) had to do a deal with the Liberal Democrats (gold) to get over the 326 seats needed to form a coalition government. The map in this form is a much more useful mechanism for communicating the results for this specific data. It tells the story far more effectively than a geographic map.

Hexagons have been used as a framework for mapping since at least 1895. They were also promoted by Danny Dorling in the 1980s as a method for mapping election results because they are close to circular (and thus pleasing on the eye) and they tesselate well, providing flexibility and six shared boundaries each. Dorling noted this was a pretty good fit for UK political geography. Oxford University recently published a blog reminding the world of Dorling's work prior to the recent election.

Sporadically, news agencies have used hexagons but this year the hexagonal cartogram went viral. Virtually everyone used them. In fact, you'd be hard pushed to find a news agency or media outlet that didn't. Andy Kirk even proposed a new name - the elecxagon map which struck me as a fun way to refer to them in this context. I modified it a little more - 'helecxagon'. So let's take a look...

The BBC got the 6 sided ball rolling with a giant physical map they built in the piazza at Television Centre. A map you could walk on. A map that had tiles added throughout the night as results came in. A map that was used for short interviews with virtual nobodies and which they panned across as they went to new bulletins. A map that was, well, rather under-used. Shame. It's almost like they didn't really know how best to use it as part of their broadcast.

BBC piazza election map

The BBC web site (and many of their other digital mapping) curiously did not go for hexagons which they had used successfully in 2010. An odd decision and with their under-used giant hex-map they dropped the ball a little in mapping terms.

Others filled their boots as the results rolled in and web maps began to be coloured in. The Telegraph used a hexagonal cartogram, as did Sky News

Sky news web map

The Telegraph election web map

The Independent went with a hexagonal cartogram too...but the web page opens with the geographic version and there was an option to switch to a geographic version if they wished.

The Independent web map

In their print media, The Independent preferred a geographical view and they also offered a slider comparative view comparing the 2010 with the 2015 results on their blog...again, geographic.

The Independent print version

The Independent 2010/2014 comparison slider

Bloomberg also gave visitors to their web site the option of a geographic or a hexagonal cartogram. What I particularly liked was the way that the map transitions between geographic and hex through animated proportional hex symbols. Largely meaningless, they did provide a subtle visual link between the abstract hexagons and the real geography. Using a transition gives the eye something to follow and it's arguable that it aids our interpretation of where places are in relation to one another.

The transition state of Bloomberg's web map

Bloomberg also had a fun animated map by Julian Burgess and Adam Pearce who used a blank canvas with no boundaries of any form, across which splodges of colour were fired. The results are animated so a map of colour builds during the 25 seconds that the animation plays. It's a piece of visual data art and one of the more interesting approaches to mapping the data. There's no way you can recover the results or explore the data but that's not the point. It's exists because they had a good idea. It works.

Ollie O'Brien produced a live map for election night that updated the results. He has since made a few post-election maps showing various metrics such as swing in share of vote, turnout etc. Plenty more discussion on his blog and a link to a web map featuring the various layers here. Ollie went for a geographical view of the results and multivariate proportional symbols.

Swing map by Ollie O'Brien

Ben Hennig couldn't settle on a particular style so went with the option of providing three versions on his maps of the results. He illustrates the geographic, hexagonal cartogram and a gridded population-equalizing cartogram side-by-side. You get three maps for the price of one with Ben's work and if nothing else it's a good way to show the different trade-offs between map type. More detail on Ben's blog and his continuing work with Danny Dorling in developing cartograms.

Three-in-one map by Ben Hennig

In my opinion The Guardian provided the most compelling and complete cartographic service on the night itself. A map that was coloured in as results came in, that auto-zoomed and panned to a constituency you could search for or click on. The live election headlines scrolled next to the map and they to were geographically enabled so clicking on the headline brought up the results for that place.

The hexagons showed regional boundaries and constituency boundaries, hover the mouse and you got some basic detail. Click and you get more.  More than that, you could switch between the overall map showing the winning party (using the traditional colours) to a map that showed majority, turnout, and vote share by party. While still using the basic cartogram, these maps used transparency (as an unclassed choropleth) and proportional symbols (arrows) well to convey the message of the different election metrics. Lots to interest both the casual reader and those more interested in digging a little deeper. Supporting graphs and tabulated results as well as subtle labels added to the overall approach and usability.

The Guardian general web map

The Guardian vote share for Conservatives web map

The Guardian turnout web map

The Guardian swing (here, to SNP) web map

And so, after the serious maps come the frivolous. There were plenty but these are the ones that caught my eye.

It soon became clear that the Scottish National Party were sweeping Scotland with a swathe of yellow constituencies. With much of the rest of England and Wales being coloured blue or red, the comparisons with Maggie Simpson began proliferating our social media feeds.

Vaughan Roderick compared the final map with a quick sketch of traditional coal mining areas of the UK. These traditional industrial heartlands are staunch Labour areas and so the visual correlation between the red of the map with areas of strong support for the centre-left party are a natural fit. The approach gives context though and helps to lift the lid on why the map is coloured as it is. Of course, voting behaviour is far more complex but this was a useful way of reflecting on some of the historical and geographical reasons for the patterns.

Combining a cartogram with the beauty of a hand-made 'physical' map, Tom Katsumi opted for a cross-stitched version, adding a stitch as the results came in to colour in his cartogram based on squares.

Finally, my colleague Craig Williams even built his own map using giant building blocks...all four of them, some days before the election. Given the result, he was remarkably close.

And what of my efforts...they're coming along nicely. I have been making two interactive maps. One an artistic effort and one built from the ground up using 3D hexagons (I'm calling them hexstones). I wasn't intending to make the maps live on the night. Instead, preferring to work on the full results after the election and taking the time to make the map I want to make.

For the 3D map I went for hexagons because I've spent years making 2D cartograms...and I wanted to tackle the technical challenges of making tesselating hexagons on a 3D, spherical world. There's also a natural metaphor with the Giant's Causeway in Ireland and part of my inspiration was this picture of David Cameron taken last year.

My 3D map as a work in progress

The artistic one was partly inspired by the Bloomberg one but I want it to also reveal the data. I'm calling it a splat map.

My splat map as a work in progress

The election was fascinating. The cartography of the election was perhaps more fascinating if you're interested in maps (and if you've read this far I'm guessing you are).

It's pleasing to see the rest of the world waking up to the value of cartograms and, in particular, the hexagon though I wonder if there will be a backlash at the next General Election? Will everyone stick with the hexagon...or twist and search for something different that tries to set them apart. By the time of the next election there will undoubtedly be a raft of new technologies that may help or hinder as well.

Guardian's Australian Election Map

Mapping election results usually brings out the worst in cartography.  The usual default is to map an arbitrary area in a single solid colour showing the winner's affiliation (think red/blue US States).  The problem with this sort of approach is the underlying 'real' geography of where people who vote actually live is missing.  The map ends up showing a severely distorted geography because it doesn't take account of the population size and distribution and so the map of US elections appears predominantly red even though Obama (blue) won. The counter is often to distort the geography to equalase the underlying problem..such as creating a population density equalizing cartogram (the so-called Gastner-Newman approach). Then there's the dot density approach, hex-binning approach and the dasymetric approach ad nauseam.

What a refreshing change, then, to see some sense by The Guardian when mapping the Australian election. Nick Evershed briefly touches on some problems with 'traditional' election maps then shows his creation...

It's a sort of Dorling cartogram with circles sized proportional to the population in that electoral area and then coloured according to affiliation.  The circles are displaced to avoid overlapping but they've added a basemap to at least give some geographical sense to the otherwise abstract representation.

I like Dorling cartograms so I am bound to like this effort.  The symbols are clear, efficient and unambiguous. Because of the nature of the population distribution in Australia the map works and the major cities become identifiable (labels would help for people to identify each of the major cities though).  In a country that has far more people crammed across more of the actual space the technique wouldn't be as effective.

I'd have preferred a larger variation in symbol size (it's difficult to see any differentiation) and a legend to tell me what amount of people are represented by the symbol sizes but kudos to The Guardian who have not simply reached for the defaults and have sought to illustrate the story with something more nuanced and thought through. They've actually showed something sadly lacking amongst many of today's rapid map-making map-makers...they've done some cartographic research and made effective use of it. Even better, their write-up briefly describes their design process and explains why other maps were discounted before they arrived at this effort.

Form, function and keeping it simple.  Simple!

Slip, slide, pan and zoom...web map interactivity

I've just finished creating a dasymetric dot density map of the 2012 Presidential election results. It's available as an interactive multiscale web map on ArcGIS Online that goes from 1:18m (where 1 dot = 1000 votes) to 1:36k (1 dot = 10 votes) which can be seen below:

 

I also made a 1:1,000,000 version of the large scale data showing 35 million dots for a huge wall map so I thought I'd use Microsoft's ZoomIt to create, well, a zoomed version which is here:

And the version at HugePic presents the work in much the same way (though you can get metrics there). The interesting thing here is the different types of useability. For the multiscale web map, each zoom level shows re-classified data so you get incrementally more dots as you move through the scales and you can click on the map to reveal data; but of course you don't ever get the impact of all the data at once. Conversely, the large wall map sacrifices some of the background detail but you can see the data at once (when it's on the wall). Every dot on a singel map but the zoomIt controls still allow you some element of interactivity to slip and slide across and within the map. If you have a view on which approach you prefer, add a comment and let me know.

The Economist ponders map types

The Economist recently asked for reader opinions on the types of map used to portray the data it uses. It focused on the choice between cartograms, choropleths and proportional symbol maps.  I added comments which are reprinted below but you should read the original article here first.


Poor mapping gives the wrong message. Most are unaware of map theory so mistakes go unnoticed; misinformation is propagated. That said, asking readers their opinion is like a doctor asking a patient what medicine they prefer. The doctor has the conferred expertise to make a sound judgment.  The same is true here so my comments are based on my professional experience to add to the mix.

Population equalized area cartograms are impactful but difficult to decipher because of massive distortions.  We’re atuned to see our world in a particular way (normally through the hideously distorted Mercator lens) so when familiar shapes are further modified we struggle.  Numerous alternatives use circles, squares, hexagons and non-contiguous areas which gives choice.  I like cartograms but am used to them, know how to construct them and don’t have difficulty in deciphering the content.  They work best for global datasets where continents can be seen.  For headline grabbing infographics then a cartogram is hard to beat but one way of giving readers visual comfort is to add a second, smaller map using a more conventional method for comparison.

Cartograms rescale geography to account for differences in size of areas used to report data values.  If a conventional map type is used that maintains geography, this difference often isn’t accounted for and the map is worthless. The classic example is the choropleth that maps totals. Consider the number of medals that Team GB won at London 2012.  Greater London has a population of 8278251 with 10 medal winners (0.12 medals per 100,000 people). Cardiff has 346100 people and 4 medal winners (1.16 medals per 100,000 people).  A map of totals shows Greater London as visually dominant and Cardiff much less so when the reverse is true. Normalized results allow proper per capita comparisons across the map that account for underlying populations.  The classification scheme used is also vital as it can dramatically alter appearance. There are many choices (natural breaks, equal interval, quantile, standard deviation etc.) and each dataset requires exploration to avoid imbuing false patterns.  Choropleths are bland but they do their job. Make good use of other design principles to combine functionality with a useful aesthetic.  Your colours are poor. Green for non-export markets confuses and neutral grey would be a better choice.  You use light peach, through orange/pink to a heavily saturated red last seen during the cold war on propagandist maps! It’s visual noise. Adding Catalonia in burgundy makes it seem part of the choropleth spectrum yet isn’t. Good colours go a long way to making the map work. Legends are important to see the classification scheme but the map should be able to tell the headline story without one. All choropleths suffer from dominant large areas so where possible use an equal area projection; and inset maps for those parts of the map that contain small geographic areas.

Your proportional symbols are too similar, leading to the impression that exports are similar.  Greater variation in symbol size would help.  Transparency deals with overlaps but won’t always work where large data values occur in smallest areas. Colours could be improved and a neutral background would help with contrast. Humans aren’t good at estimating differences between areas.  How many people can accurately tell if one circle is double the size of another? There are ways to adjust for our underestimation but which introduces further complexity.

You might consider dot density, dasymetric  or, for this subject a flow map would suit.  Flow lines from Catalonia to neighbouring countries could be scaled by width to indicate proportions.  My rudimentary reworking of Minard’s flow map of British Coal Exports shows how flow can be represented. If you’re presenting maps online then consider hover and click events to reveal data values or additional information. This pairs back the map to essential graphics while allowing people to delve into the content interactively.

So the answer isn’t straightforward.  Consider each dataset independently of preconceived ideas about map type.  Think about the story you want to tell to inform your choice.  Once chosen, the next trick is to design it to work effectively and marry form and function meaningfully.  This isn’t easy and is the main reason why so many poor maps are made. Sometimes a table or a graph is much more useful.  Sometimes you might combine graphs with the map or combine map types. The map should be informed by a decisions that bring together useful graphic components in a well-thought out composition. There’s no substitute for looking at how others tackle thematic cartography. Learn what works, understand what doesn’t and your maps will evolve into purposeful products regardless of map type.