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Geographic Information Systems (GIS)

This guide provides an introduction to GIS software, data, and resources.

GIS Data Formats

GIS Data comes in several different formats:

  • Vectors: geographic features of the same type are stored in a file as strings of coordinates that form points, lines, or polygons (areas) in conjunction with attributes that describe the features. Vectors are drawn to a specific scale with a particular coordinate system and map projection that allows them to be depicted visually and overlaid with other geospatial data. Common formats include shapefiles, geopackages, and GeoJSON.
  • Rasters: a continuous surface of grid cells of equal size, where values of a cell denote a feature type or attribute and the size of the cells indicates resolution. They are structured like other digital images except they are georeferenced: rasters have been created or warped to a particular coordinate system and map projection so they can be overlaid with other geospatial data. Formats vary widely.
  • Tables: each record represents a geographic feature with attributes (columns) that describe that feature, but the records lack geometry and cannot be displayed visually. To visualize tables, the records can either be joined to a corresponding vector file of the same features using a shared unique identifier, or can be plotted as a point-based vector if the records include attributes for XY coordinates. Common formats include delimited text (CSV, TSV) and spreadsheet files.
  • Spatial Databases: containers that hold a collection of vector, raster, and tabular data. Depending on the GIS software you use, you access the databases by establishing a connection to them or navigating them the way you would a file folder. Common file-based formats include: file geodatabases (gdb, default ArcGIS format), personal geodatabases (mdb older ArcGIS format), and Spatialite (open source).

Large Catalogs of GIS Data

Global GIS Data

US GIS Data

Census TIGER File Generalization Comparison

Rhode Island GIS Data