This column lists a few top resources for geospatial data on the internet. See tips on finding spatial data at "Locating spatial data." Please also feel free to get in touch with your data questions.
See an extensive listing of resources by country at the International GIS Data Research Guide.
Where does spatial data come from?
|Type of Producer||Example|
|Inter-governmental organizations||United Nations Environmental Programme|
|Researchers and research centers||U.S. Congressional District Shapefiles|
|Non-profits||World Resources Institute|
Where can you search for spatial data?
|Type of site
|Library research guides||International GIS Data|
|Open data sites||datacatalogs.org|
|Try searching for your topics, plus "shapefile" or "spatial data"|
Vector data represent discrete features, which could have names or attributes. It is often used in social science research to describe things with clear boundaries. Vector features can be of three types:
|Point:||A single pair of coordinates, like a cell phone tower or a crime scene|
|Line:||Something that has length but not width; often a road or a river|
|Polygon:||An area with boundaries; often a political feature such as a state or county, but could also be a lake, building footprint, etc.|
Common formats: shapefile, KML or KMZ,GeoJSON, MIF, GPX
Examples: Census TIGER Products
Raster data represent continuous features as cells (pixels) in a grid, much like image files in which each pixel has a location in space plus a meaningful value. Raster files are frequently used in scientific studies for phenomena like rainfall, elevation, or things that vary continuously in space.
The level is detail is expressed as the cell size, or spatial resolution.
Common raster file formats: TIFF, Esri GRID, IMG, and others
Examples: National Elevation Dataset
Attribute data are not really a separate kind of data, but rather the fields (numeric or text) that can be joined to features. The columns in the table become the attributes of the geographic feature to which it corresponds.
The trick is finding a unique identifier common to the features in the shapefile and the rows in the table. Common identifiers include FIPS (for the U.S.) and ISO-3166-1 (for countries).
Common formats: ArcGIS can join together geographic data like shapefiles with tabular data in formats such as .xls, .mdb, .txt, or .csv, using the Join tool.
Examples: Census 2010 Data
A gazetteer is a geographical dictionary that frequently lists placenames along with identifying information. While not necessarily in digital format, gazetteers in machine-readable formats like CSV, accompanied by latitude and longitude, can be converted to spatial data using the Add XY Data tool in ArcGIS.
Web services provide a live connection to a remote databases via GIS software, without downloading the data to your local system. Different varieties of web services allow different capabilities for working with the data.
To use web services in ArcGIS, you must connect to the service via the Catalog window.
Example: ArcGIS Online