HCI my projects Web 2.0 Work in IT

Aggregated values on a Google Map

UPDATE 27/08/09: The functionalities of my version of MarkerClusterer have been included in the official Google code project, you can find it gmaps-utility-library-dev. The most interesting part was the so called MarkerClusterer.

Imagine you need to show thousands of markers on a map. There may be many reasons for doing so, for example temperature data, unemployment distributions, and the like. You want to have a precise view, hence the need for a marker in every town or borough. What Xiaoxi and other developed, is a marker able to group all the markers in a certain area. This is a MarkerClusterer. Your map gets split into clusters (of which you can specify the size – but hopefully more fine grained ways of defining areas will be made available) and you show for every cluster a single marker, which is labelled with the total count of markers in that cluster.

I thought that this opened a way to get something more precise and able to make reasoning over map data. Once you have a ClusterMarker, wouldn’t it be wonderful if you had the possibility of displaying some other data on it, rather than the simple count? For example, in the temperatures distribution case, I would be interested in seeing the average temperature of the cluster.

That’s why I developed this fork of the original class (but I’ve applied to get it into the main project – finger crossed!) that allows you to do what follows:

  • create a set of values to tag the locations (so that you technically attach a value to each marker)
  • define a function that is able to return an aggregate value upon the values you passed, automatically for each cluster

That’s all. The result is very simple, but I believe it is a good way to start thinking about how the visualization of distributed data may affect the usability of a map and the understanding of information it carries. Here’s a snapshot of the two versions, the old on the left (bearing just the count) and the new on the right (with average data). Data here refer to NHS Hospital Death Rates, as published on here. If you want to see the full map relating to this example, click here.