Vector Formats (Continued)
Spatial Data Transfer System (SDTS) - SDTS, a new transfer format developed by the US government, was designed to handle all types of geographic data. SDTS can be either binary or ASCII but is generally binary. Virtually all geographic concepts can be encoded in SDTS, including coordinate information, complex attribute information, and display information. This versatility causes a corresponding increase in complexity. To simplify things, several standard subsets of SDTS have been adopted. The first of these, the Topological Vector Profile (TVP), is used to store certain types of vector maps. SDTS can also be used for raster information. Not much data is available in SDTS format at this time, nor do many software systems support it. However, it will be the foundation of the US National Spatial Data Infrastructure (NSDI). Its importance will increase as more NSDI data becomes available.
Topologically Integrated Geographic Encoding and Referencing Files (TIGER).- TIGER is an ASCII transfer format used by the US Census Bureau to store the street maps constructed for the 1990 census. It contains complete geographic coordinates and is line, not polygon, based (although polygons can be constructed from its attribute information). The most important attributes include street name and address information. TIGER does not contain display information. Maps of the entire US are available in TIGER format.
Vector Product Format (VPF) - VPF is a binary format used by the US Defense Mapping Agency. It is well documented and can be used as an internal format and as a transfer format. It carries geographic and attribute information but no display data. VPF files are sometimes referred to as VMAP products. The Digital Chart of the World (DCW) is published in this format.