Shapefile Overview

The Shapefile is an industry standard introduced by ESRI which published the Shapefile specs a long time ago.  The Library of Congress has a detailed description of the format.  Almost all of the vector GIS data available on the web is in shapefile format.

A shapefile actually consists of at least three binary files, and you must keep all three files together. 

    The SHP file, with the coordinates.  These are stored in binary format, but can be displayed in human readable text.  The SHP file also has a header for the entire layer, and a header for each record.

The SHX file, an index.  These are stored in binary format. This contains:

  • File header, identical to that in the SHP file.
  • Bounding box for each record
  • The offset to the start of each record, its length, and the number of parts and points.
The DBF file, a dBase file with the database table containing record attributes.  This links to the shp and shx files implicitly by the implicit record number in the DBF file.  This is a very old format, and databases have gotten much better, but all GIS software likes it, and no alternative has anywhere near the acceptance.

There may be additional files, but they are not standard and not documented in the ESRI specs.  MICRODEM does not generally use these additional files. Because MICRODEM will only use shapefiles in Lat/Long coordinates in WGS84, it is not necessary to use the extra files.  One of the extra files is the projection (PRJ file, with the projection and horizontal datum).  The absence of required projection information is the biggest flaw in the shapefile specification.  If you need to make a PRJ file, you can use

Shapefiles in MICRODEM must be lat/long on WGS84.

You should consider SHZ format to avoid separating the parts of a shapefile.

Recover shapefile geometry.

ESRI has a new proprietary format for data, which is fine if you drink the cool aid and only want to live in the ESRI ecosystem.

Last revision 6/11/2020