Mapping Baltimore's Open Data


2 min read

We just added three new MBTiles of Baltimore city to, all designed using the data released earlier this year by the city of Baltimore on OpenBaltimore, an open data portal for hosting public datasets. The city’s initial release included a variety of geocoded datasets, with more data on the way. Developers interested in taking these datasets to build visualizations and applications will need maps to provide context for the data, so we decided to design a few maps using TileMill to show what is possible using the public shapefiles.

Baltimore Light

The goal with this first map was to create a clean baselayer well suited for visualizing data. The shapefiles Baltimore released go beyond map essentials like roads and bodies of water to also include building footprints and vegetation. These shapefiles gave me more to work with when designing the look and feel of the map and help give a clearer picture of the city.

Baltimore Dark

In order to design a dark variation on the first map, I started by setting up color variables in my Carto stylesheet for the first map. Then I duplicated the map, making it possible to radically change the map style with ease.

Baltimore Retro

Lastly, I took a more creative route and built a stylish map of Baltimore inspired by old print atlases. Most of the layers are filled with halftone bitmap image patterns, with a couple overlay layers on the whole map to give it a weathered tone and papery texture. With the help of Carto pseudo elements, I applied multiple colors and styles to map features within single layers, easily implementing complicated textures and styles. If you zoom in, you can see unique icons for parks, rail yards, bodies of water, and cemeteries that I made in Inkscape and then added to the map as center points to elements on the Baltimore land use shapefile.

All of these maps were made using TileMill, our open source map design studio. If you have questions about making maps with TileMill, check out for documentation or to ask a question.

What we're doing.