United States Congressional District Shapefiles This site provides digital boundary definitions for every U.S. Congressional District in use between 1789 and 2015.
U.S. Census Bureau
Maps and Data Find geographic data and products such as the TIGER/Line Shapefiles, KMLs, TIGERweb, cartographic boundary files, geographic relationship files, and reference and thematic maps.
Baltimore Open City GIS Data is Baltimore's public platform for exploring and downloading open data, discovering and building apps, and engaging to solve important local issues. Analyze and combine Open Datasets using maps, as well as develop new web and mobile applications.
MD iMap Main portal for state wide spatial data on a wide range of themes.