Vector Formats
Many GIS applications are based on vector technology, so vector formats are the most common. They are also the most complex because there are many ways to store coordinates, attributes, attribute linkages, database structures, and display information. Some of the most common formats are briefly described below:
Arc Export - Arc Export is a transfer format, either ASCII or compressed into binary used to transfer files between different versions of ARC/INFO. It is undocumented and will work only with ESRI products.
ARC/INFO Coverages - An ARC/INFO "coverage" is a set of internal binary files used by ARC/INFO, a GIS program. This file format is proprietary and not readily usable by other programs.
AutoCAD" Drawing Files (DWG) - DWG is the internal, proprietary format used in AutoCAD® software, which is a computer-aided design/drafting (CAD) program. Despite its proprietary nature, AutoCAD can convert any DWG file to a DXF file (described below) without loss of graphic information. As with DXF files, there are a number of ways to store attribute information in DWG files. The emerging standard is one that uses Extended Entity Data (EED) to link attributes, but many others are possible. However, the lack of one standard for linking attributes can cause problems when data is transferred between systems.
Autodesk’s Data Interchange File (DXF) Format - DXF is probably the most widely used vector data transfer format, and a file in DXF format offers some very strong advantages. It contains very complete display information, and almost every graphics program can read it. However, there are several different ways to store attribute information in DXF and to link DXF entities to external attributes. Because there are no attribute standards, many programs that claim to read DXF files still do not import attribute information properly.
Digital Line Graphs (DLG) - DLG, a transfer format used by the US Geological Survey (USGS), depicts vector information portrayed on printed paper maps. It carries very accurate coordinate information and sophisticated feature-classification information but no other attribute data. DLG does not include any display information. The DLG standard is significant because the USGS and other US government agencies have used it to publish large numbers of digital maps.
Hewlett-Packard Graphic Language (HPGL) - HPGL is a language that controls computer plotters; it contains display information but no geographic coordinates or attribute data. It is usually not appropriate for the storage or transfer of GIS data.
MapInfo" Data Transfer Files (MIF/MID). - MIF/MID is a transfer standard used by MapInfo, a desktop mapping system. It carries all three types of GIS information: geographic, attribute, and display. Attribute links are implicit in the file format.
MapInfo Map Files. - MapInfo has its own internal binary format, known as a map file. It is undocumented and proprietary, so it cannot be used outside a MapInfo system.
MicroStation Design Files (DGN).- DGN is the internal format used by Bentley Systems Inc.’s MicroStation, a CAD program. It is well documented and standardized, so it may also be used as a transfer standard. DGN files contain detailed display information. The most common way to store attributes is to place them in an external database file and record links in the MSLINK field-a data item carried for each element in the DGN file.