File Formats for GIS Data

Vector Data:

• Shapefile
  • Developed by ESRI for ArcView GIS
  • Specification is readily available; supported by other software
  • Does not support the storage of topological information
  • Can only store one feature class
  • It is a collection of 3 or more files:
    • Required files:
      • Main file: .shp
        • This is the primary file that stores feature geometry.
        • "It's a direct access, variable-record-length file in which each record describes a shape with a list of its vertices." (ESRI)
        • Stores integer and double-precision numbers (ESRI)
      • Index file: .shx
        • Stores the index of the feature geometry.
        • "Each record contains the offset of the corresponding main file record from the beginning of the main file." (ESRI)
      • Dbase table: .dbf
        • Stores the attribute data for features contained in .shp, with one record per feature.
        • There is a one-to-one relationship between geometry and attributes, which is based on record number. Attribute records in the dBASE file must be in the same order as records in the main file.
        • It is a mix of binary and ASCII data. Header contains binary data. The records are all in ASCII. (XBase)
    • Optional files:
      • Projection file: .prj
  • Sources:
    • ESRI Shapefile Technical Description: http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf
    • XBase database Format: http://www.clicketyclick.dk/databases/xbase/format/dbf.html#DBF_STRUCT
    • GIS File Formats: http://www.giscentrum.lu.se/english/whatisgisFileFormat.htm

• Coverage
  • Developed by ESRI

-- AprilWebster - 12 Mar 2007