Much vector data is stored in conventional GIS formats, such as those of ESRI SHP or MapInfo formats. However, there are a number of vector data formats which are specific to particular data types and US agencies. These are important because they are the format in which a large amount of public-domain data is distributed. , such as those of ESRI SHP or MapInfo formats. However, there are a number of vector data formats which are specific to particular data types and US agencies. These are important because they are the format in which a large amount of public-domain data is distributed. It contains mostly cartographic features like political boundaries which aren’t much use for realistic terrain visualization. There are many free Shapefiles for global political boundaries, but surprisingly they are all quite deeply flawed in many respects, as detailed in the very impressive 4-part blog entry beware: pretty much all of the USGS data that says NAD27, can actually mean OHD, NAD27 Alaska, NAD27 Aleutians, or NAD27 CONUS, depending on where the data actually is. It’s possible for a road to have no attribute codes, or many. The data is highly variable. Most (like 99%) have only the ‘road class’ attribute, which doesn’t tell you much. However, i have encountered a single road with all of the following: TIGER/Line (‘Topologically Integrated Geographic Encoding and Referencing’) files contain geographic features: roads, railroads, rivers, lakes, political boundaries, census statistical boundaries, etc. covering the entire United States each county is represented by a directory of files with a common basename, and different extensions – for instance, county 9 in state 23 (Maine) consists of the following files: TGR23009.RT1 TGR23009.RT2 TGR23009.RT3 TGR23009.RT4 TGR23009.RT5 TGR23009.RT6 TGR23009.RT7 TGR23009.RT8 TGR23009.RT9 TGR23009.RTA TGR23009.RTC TGR23009.RTH TGR23009.RTI TGR23009.RTP TGR23009.RTR TGR23009.RTS TGR23009.RTZ Provides free geospatial data for highways, railroads, and all other kinds of transportation, for all of North America. Historically, this was in their own ASCII file format. ) is it extremely low detail. VMAP1 should be available, but only an early version of a few tiles has actually been released (see ). Making the full (public domain) VMAP1 actually available will apparently require a very painful, expensive legal process involving the FOIA (Freedom Of Information Act), which (as of 2006) nobody has yet done. Source.