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Geographic Information Systems (GIS)

A guide to tools, data resources, and training for GIS at the Library

Geospatial data formats

Vector    
File type File extension(s)  
Shapefile 
(a package of several separate files)

Mandtory files

.shp gives features their geometry (points, lines, polygons)

.shx is a mandatory Esri and AutoCAD shape index position file

.dbf is a mandatory standard database file used to store attribute data and object IDs

Optional files

.prj contains the metadata associated with the shapefile's coordinate and projection system

.sbn is an optional spatial index file that optimizes spatial queries

.sbx are similar to .sbn files in which they speed up loading times. It works with .sbn files to optimize spatial queries

.cpg are optional plain text files that describe the encoding applied to create the shapefile

 

 
Esri File Geodatabase  .gdb is folder containing all the files of the geodatabase  
Geopackage .gpkg is a open source (SQL lite) package format for sharing geodatabase files  
QGIS .qgs and .qgz (zipped)  
Keyhole Markup Language .kml and .kmz (zipped) files were originally developed for Google Earth and are now an Open Geospatial Consortium standard.  
     
Raster     
File type File extension(s)  
GeoTIFF

.tiff is the raster (image) file

.tfw is the text file accompanying the .tiff that includes the georeference information

 

 

There are many more file types that can be used on GIS platforms. The Wikipedia entry on GIS file formats has a fairly extensive list, and Esri documentation can provide more information about their proprietary formats. 

Georeferencing raster data

Georeferencing is the process of associating a raster map (an image file) with a known geospatial coordinate system. You might think of this as "pinning" a map image in place on top of a larger map grid with latitude and longitude points. Georeferncing is often of a part of working with historic maps in order to compare them to present-day geographic features.