From the webpage:
Welcome! In this short guide we share some insights and tips for making thematic maps. Our goal is to cover the important concepts in cartography and flag the important decision points in the map-making process. As with many activities in life, there isn’t always a single best answer in cartography, and in those cases we’ve tried to outline some of the pros and cons to different solutions.
This is by no means a replacement for a full textbook on cartography; rather it is a quick reference guide for those moments when you’re stumped, unsure of what to do next, or unfamiliar with the terminology. While the recommendations on these pages are short and not loaded with academic references, please appreciate that they represent a thoughtful synthesis of decades of map-making research.
This guide was written by Axis Maps, adapted from documentation written for indiemapper in 2010. However, the content here is about general cartography principles, not software-specific tips. To see the material in its original context, visit indiemapper and its help pages.
If that doesn’t sound exciting, perhaps this will:
Thematic maps are meant not simply to show locations, but rather to show attributes or statistics about places, spatial patterns of those attributes, and relationships between places. For example, while a reference map might show the locations of cities, a thematic map might also represent the population of those cities. It’s the difference between mapping places and mapping data. This site is about thematic maps, describing some of the different types and basic principles.
Hmmm, data about places? Relationships? That’s starting to sound suspiciously like a topic map expressed in a different vocabulary.
The same principles apply, in addition to places on a geographic grid, you can have subjects that exist only on your own intellectual grid, arranged in relationships as you see fit.
Over the years you have no doubt seen a number of offenses against the art of presentation in the name of topic maps. You have the power to break from that tradition. Seeing what works in other mapping domains is one place to start.
Where else would you look for fresh ideas and themes?