Polymaps uses Scalable Vector Graphics (SVG) to display information on top of existing maps. Because the data can be loaded at a range of scales, the information can be shown at many levels, from Country level down to individual streets. Designers and developers can style and design the data using Cascading Style Sheets.
Users can set which direction is north on a map, zoom in to see the quality of a street surface and group data into clusters. Static map images can be overlaid with data sets and colorful presentations using vector data.
To publish information on map images, Polymaps uses the spherical mercator tile format. The what? To quote from the Open Street Map wiki, “QuadTiles are a geo-data storage/indexing strategy. The idea is to store a geo-database such that data for a specific location can be retrieved quickly, by dividing the data up by location, partitioning the world into tiles.”
Here’s a few examples from the site showing some ideas of how you might use the tools for your own needs:
These maps of the United States show unemployment rates in over 3000 counties using a choropleth map. Users can zoom in for higher resolution and to see county names and numbers. The map background is a monochrome image layer from CloudMade.
A cluster map is used to visualize discrete events across time and space. This map uses k-means clustering to coalesce dots and visualize the density of crime in Oakland.
Customized San Francisco map constructed using a single image layer of CloudMade tiles.