Since the arrival of Google Earth there has been a lot of interesting Geo-Data Visualization projects where the overlay of data becomes useful in communicating key issues to the public at large. A great example of this approach is this 3D exploration of air pollution in London.
In July 2006, an interactive three-dimensional map that allows users to "fly" above London to see pollution hotspots was launched by the Centre for Advanced Spatial Analysis (CASA) - University College London and King's College. The easy-to-use tool allows transport and urban planners, as well as the general public, to zoom in on different areas to see how clean particular neighbourhoods are. It is the first time air pollution for an entire city has been related to the built environment. The map also provides projections of air quality up to 2010, taking into account measures adopted at local and national government levels to improve the air Londoners breathe, such as the uptake in catalytic converters and constraints on factory emissions.
The London Air Quality Network, which hosts the web-based map, was aware that two-dimensional representations can be difficult for non-specialists to grasp, and so seized upon UCL CASA's suggestion to use their expertise in 3D mapping to create a simple but effective tool. Users can already choose to focus on roads and railways, the River Thames, green spaces and the congestion charge zone. Air quality can be viewed by overall level of pollution, or by key pollutants such as the particulate matter PM10 or oxides of nitrogen.
There's also a great video on YouTube that provides a fly through London and its polluted arteries.