Reference

Last updated on 2026-10-17 | Edit this page

Glossary

3-2-1 rule
A backup guideline: keep three copies of data, on two different types of storage, with one copy off-site.
Attribute
A piece of information about a feature, stored as a column in the attribute table.
Checksum
A short code calculated from a file’s contents; if the file changes, the checksum changes.
Coordinate reference system (CRS)
The datum, coordinate system, units and (for projected systems) projection that link coordinates to places on Earth.
Data dictionary
A table describing every field of a dataset: name, meaning, type, length, allowed values and null rules.
Data management plan (DMP)
A document describing what data a project will create and how it will be handled, shared and preserved. NSF calls it a Data Management and Sharing Plan.
Data model
A way of representing the world as data; the two main geospatial data models are vector and raster.
Datum
A model of the Earth’s shape and its position, such as WGS 84 or NAD83.
Domain
The set of values a field is allowed to hold, often presented as a dropdown list.
EPSG code
A numeric identifier for a coordinate reference system, such as EPSG:4326 or EPSG:26916.
Foreign key
A field in one table that refers to the primary key of another, used to join or relate them.
GeoPackage
An open, single-file format (an SQLite database) for vector layers, tables and rasters; an OGC standard.
Geographic coordinate system
A CRS that uses latitude and longitude in degrees.
GeoTIFF
A TIFF image with georeferencing information built in; the standard raster format.
Lineage
The record of where data came from and how it was processed; also called provenance.
NoData value
A special raster value meaning “no information” for a cell.
Primary key
A field that uniquely identifies each row of a table.
Projected coordinate system
A CRS that flattens the Earth onto a plane, with coordinates usually in meters or feet.
Raster
Data stored as a grid of equal cells, each with a value.
Relative path
A file location given relative to the project folder, so a project still works when the folder is moved.
Reprojecting
Calculating new coordinates for data in a different CRS (as opposed to defining which CRS existing coordinates are in).
Resolution
For raster data, the ground size of one cell.
Shapefile
An older, multi-file vector format (.shp, .shx, .dbf, .prj and others) with limits on field names, size and data types.
Topology
The spatial relationships between features, such as shared boundaries and connected lines.
Vector
Data stored as points, lines or polygons, each with attributes.
Version control
A system for recording changes to files over time, such as numbered versions with a change log, or Git.

Further reading