In the recent Visual Analytics workshop at ISB, I introduced map charts and illustrated their use with the interactive visualization tool TIBCO Spotfire.
Map charts are data visualizations that combine a geographical map with a dataset that has information about geographical entities. For example, census-type data at the district level. The data are then displayed on top of the geographical map, such that coloring and other features can be used to represent a measurement of interest.
To create a map chart, one needs to obtain “shape files” which are a set of files with extensions such as .shp and .dbf. Shape files are available for purchase from various websites, and are freely available on others. One source that provides free shape files for many countries is DIVA-GIS. The administrative files for India include shape files at 4 levels:
- files with “0″ refer to country-level, and will create a map of
- India as a whole
- files with “1″ refer to state-level, and will create a map of India with boundaries between states
- files with “2″ refer to district level, and will create a map of India with boundaries between districts
- files with “3″ refer to sub-district level — this will create a map with sub-district level boundaries, as shown in the image.
Sub-district level map of India, generated from DIVA-GIS shapefiles
The choice of files to use therefore depends on the geographical level of your data. If the data are at the state-level, use the files with “1″.
All this is technically straightforward, but there is another issue that creeps up: What if the available shapefiles include some sensitive borders or disputed territories? Since the data analyst is the one obtaining the shapefiles (the software companies are smart not to provide them!), it is his/her responsibility to make sure that the shapefiles are appropriate for the intended audience.
