In my last post about [TileMill](http://www.pbs.org/idealab/2010/08/tilemill-custom-maps-to-help-with-data-dumps-hyper-local215.html), I outlined some of our general plans and the background for why we’re working on this project to help make it easier for people to design very custom maps online. One question that we get a lot from people who are new to the GIS space is, “When would I need this? How could I hope to improve on what (fill in the blank: Google/Bing/etc.) make available?”
The answer is that it’s all about the details of the specific communications goal you want to accomplish. In many cases, Google and Bing maps are great. In other situations, having additional control over map design is crucial to reach your goal (or at least improve your delivery). To get a sense of the kind of situations where custom designed maps really make a difference, I’ll share a story about some maps that we made for our hometown of Washington, D.C.
In 2008 the Washington, D.C. Office of the Chief Technology Officer (OCTO) released a large set of municipal datasets to the public to coincide with the original “Apps for ____” contest, [Apps for Democracy](http://www.appsfordemocracy.org/). Included in this data were [ESRI shapefiles](http://en.wikipedia.org/wiki/Shapefile), a great format for GIS pros but hard to work with for anyone else. Using this same geodata, we created three very different custom maps, each for different use cases.
The first was for a website we called [StumbleSafely](http://outsideindc.com/stumblesafely/). It was a bit tongue-in-cheek — the idea was that the site could help users see the latest crimes near their favorite bars so they could be aware of problem areas. Because we weren’t actually helping people map out navigation paths to get home, the real communications point we wanted to hit with the map was showing crime in proximity to bars and subway stations. Street names didn’t matter as much, and neither did highlighting any other kinds of businesses.
The D.C. police department was publishing crime data that we could scrape and add to the site to show crime locations, and the Alcoholic Beverage Regulation Administration was publishing liquor license data that we could use to visualize density points on a map that corresponded to areas with lots of bars. For the base map itself, though, we needed little else in the way of data to accomplish our purpose. We were able to take shapefiles for roads, parks, and river features in the city and do a very low key map design that fit the aesthetic of the site and contained no extraneous information. People familiar with the city could quickly look at it and see right away what the crime situation was like in their favorite areas, without any other distractions.
- DC Bikes
Another example was a very similar map, but for a very different use case. [DC Bikes](http://outsideindc.com/bikes) was designed on the same platform as StumbleSafely to provide a resource to the D.C. cycling community. It showed bike thefts, bike lanes, and bike shops around the city.
For the map on that site, we again wanted to show crime data and were able to take the same basic approach to StumbleSafely for the base map design, but there was one additional feature we needed — bike lanes. These were made available as a shape file from the D.C. government as well, so we were able to quickly repurpose the map from Stumble Safely, tweak the colors to match a new design, and highlight the bike lanes in a new color so they stood out. For the cycling community, we were again able to show just the more relevant information on the map and omit any distractions.
- DC Nightvision
Finally, we wanted a much higher level of detail for a different project. Rather than omit details from our map in this case, we wanted to pack it full of details about public infrastructure. Not just buildings and roads, but even crosswalks, medians, and topography lines. The map we released for the public, [“DC Nightvision,”](http://demo.mapbox.com/dc-nightvision.html) includes all of these details, each of which are again published by the D.C. government as shapefiles.
With the increasing availability of shapefiles like the ones mentioned here, TileMill will make it easy for end users without a lot of GIS training to churn out custom maps that meet their unique communications needs. With the data in hand and user-friendly tools to work with it freely available, creativity will be the only limit for creating great custom maps.