interactive web map (built by ITO World) of the deaths and injuries from road traffic accidents 2000-2010 in Great Britain. That's nearly 33,000 killed and 3 million injured people...represented as separate points on the map.
Viewing the overall picture at zoom level 4 (a scale of about 1:36m) we see the all too familiar mass of points on a web map with a legend that doesn't relate to the map we're seeing. Points overlap and coalesce. It shows very little other than the fact that there's an awful lot of death and injury. At this scale the data need aggregating in some sensible way. For instance, cluster analysis would spatially summarize the data and could be mapped using an isopleth technique for a more suitable small scale map. At any of the lower zoom levels (smaller-scale) the map is less useful still.
I've never been able to zoom in further than level 15 since it fails to draw any symbols beyond that scale but what can we take from this map in terms of its cartography? The importance of designing for specific scales cannot be underestimated. Putting a mass of points on a map simply doesn't work at most if not all scales. At smaller scales, data needs manipulating so it is in a form suited to a small scale thematic map type. At larger scales, symbols need to be simple and clear. That said, I like the map for one simple reason...it's one of the first I have seen that has attempted to show a very complex data set by type rather than the use of a single coloured generic marker symbol. At larger scales the symbol design is generally good and gives a mechanism to visually disentangle incidents by type, transport, age, date and gender. It's doing what cartography was designed to do..allow the map maker to take complex data and classify, symbolize and provide a picture so patterns can be seen that goes beyond what a table, graph or uniform point marker web map can provide. It's not perfect as I've pointed out but it's pleasing to see web maps begin to show signs of cartographic thinking and design.