The National Transportation Atlas Databases (NTAD) is a set of transportation-related geospatial data for the United States. The data consist of transportation networks, transportation facilities, and other spatial data used as geographic reference. The 2001 NTAD is distributed in shapefile format. A Shapefile is a simple, non-topological format for storing the geometric location and attribute information of geographic features. Distributing spatial data in shapefile format guarantees that the data will be easy to use and widely portable, as shapefiles can be easily imported into all major GIS software platforms. Each transportation layer is distributed with five files, three of which comprise the shapefile and the accompanying attribute data. These files are of the following types: .shp files store feature geometry; .shx files store the index of the feature geometry; and .dbf files store the attribute information for the features. The other files distributed with each layer are the metadata files, distributed in text (.met) and HTML (.htm) format. Note: linear networks are distributed with two sets of .shp, .shx, and .dbf files, one set each for nodes and line features. Any errors or inconsistencies identified within any data set are documented in the CD-ROM User Notes. Once identified, corrected files are posted to the appropriate data set web page. The data here are the most recent versions available to the general public. A complete set of the data on CD-ROM is also available. The 2001 NTAD is also available in the ASCII format in which it was previously distributed. Write to answers@bts.gov to obtain the data in ASCII format. (A)
Samenvatting