Here we endeavor to give simple definitions for common GIS-related terminology and acronyms.  If you have access to this google doc, feel free to add more entries, and leave the definition blank if you’d like someone else to define it.

Coordinate Reference System – (“CRS”, “spatial reference system”, “coordinate system”) A definition of how to interpret a given set of coordinates.  See Projected Coordinate System and Geographic Coordinate System.

Coordinate Pair – An “x,y” set of numbers that describe a location. A pair of longitude/latitude measurements would describe a point in a geographic coordinate system, while a “easting and northing” could define a point in a projected coordinate system.

Datum – A mathematical model of the earth, stemming from a single point (datum) at the center of the earth and extending through a spheroid model of the earth’s surface. Modern latitude and longitude coordinates are all based on a datum.  See NAD83, NAD27, and WGS84.

Decimal Degrees – A common and very easy-to-use format for managing latitude and longitude coordinates.  For example, 43° 33' 24” (latitude), -90° 53’ 21” (longitude) becomes 43.5567, -90.8892. Use for simple conversions.

Degrees Minutes Seconds – Most well-known latitude/longitude format, often notated as DD° MM’ SS”.  Not very easy to handle within GIS technology.  See Decimal Degrees.

Delimited Text File – A simple method for storing tables in a textual format. Each data field is “delimited” with a specific character (often a comma), and each line in the file is a distinct row in the table.  Generally distributed as a .csv, or “comma-separated values” file.

DEM – (Digital Elevation Model) A dataset that describes the elevation of a given area. Generally DEMs are distributed as rasters, where each cell contains an elevation value (in meters or feet).

ESRI – Environmental Systems Research Institute, the leading name in proprietary GIS software, creators of the ArcGIS software suite, and of the now-openly-accessible shapefile data format.

Feature – a discrete vector object within a vector layer. A layer can have any number of features, and can have any number of attributes attached to it. Depending on the type of the vector layer, a feature may be a point, line, or polygon (or a complex polygon, i.e. having (a) hole(s), multiple parts, or both)

FOSS – “Free and Open Source Software” any software developed in an open source manner, and published under one of the many official open source licenses.

GDAL/OGR – A set of open source tool libraries for spatial data.  GDAL (Geospatial Data Abstraction Library) deals chiefly with raster data while OGR deals with vector data. QGIS uses these libraries for its data processing abilities.

Geographic Coordinate System (GCS) – A coordinate system in which coordinates are stored as latitude/longitude values.  These values must be based on a datum (see Datum).  Data that is stored in a geographic coordinate system can be world-wide, but spatial measurements (like the calculation of areas or distances) can not be accurately done because degrees, the unit of measure in a GCS, do not represent consistent distances around the globe.

GIS – (Geographic Information System) A database system designed to store, manage, and view data in a geographic or “spatial”, manner (i.e. “on a map”).

GDAL/OGR – A set of open source tool libraries for spatial data.  GDAL (Geospatial Data Abstraction Library) deals chiefly with raster datasets, while OGR deals with vector datasets. QGIS uses these libraries for its data processing abilities.

Latitude & Longitude – Degree coordinates, used in a geographic coordinate system. For example: N43° 33' 24”, W90° 53’ 21” (see Degrees Minutes Seconds) or N43.5567, W90.8892 (see Decimal Degrees).  In notation, N means north of the equator (S for south), and W means west of the prime meridian in Greenwich, England (E for East). Alternatively, negative coordinates are used to denote S and W (so W90.8892 becomes -90.8892).

Layer – An instance of a file or dataset which has been loaded into a GIS. Layers are stacked vertically and may have complex styling applied to them to change the way the source data is rendered. It is important to understand how a layer differs from the data represented by that layer. For instance, styling a layer does not modify the source data, nor does duplicating a layer equate to duplicating the source data.

LiDAR – (Light Detection and Ranging, from RADAR) a sophisticated remote-sensing technology that employs high-grade lasers and optical sensors. Laser pulses are emitted, collected & analyzed to produce a point-cloud of complex data, from which discrete datasets (like a DEM) can be derived.

Matplotlib – a plotting library used by QGIS to render spatial data in the map canvas.

NAD27 – North American Datum 1927, datum developed for North American in 1927, often still found on USGS maps

NAD83 – North American Datum 1983, datum developed for North American in 1983, current standard for data collection on this continent

NAIP  National Agricultural Imagery Program, a USDA program which acquires and publishes ‘leaf-on’ (growing season) orthoimagery.

NLCD – National Land Cover Dataset, raster data showing 30m resolution land cover classification for the entire US, published by USDA/NRCS - National Geospatial Center of Excellence.

NRCS – Natural Resource Conservation Service, government entity that provides free access to many governmental data resources, and publishes the NLCD (with USDA)

Plugin – An extra software component written to supplement an existing platform.  QGIS has many extremely useful plugins, written by contributors around the world.

Projected Coordinate System (PCS) – A coordinate system based on a projection, in which the x, y coordinates describe distances (in units, like meters or feet) from the 0,0 origin (bottom left corner).  Examples of common projected coordinate systems would be UTM Zones, State Plane Zones, or the Wisconsin county systems.

Projection – A mathematical manipulation of some part of the globe to create a “flattened” surface (like a paper map). Through this process, latitude/longitude coordinates are converted to x,y coordinates on the new plane.  Therefore, each projection must be based on a datum (see Datum). Similarly, projections can only faithfully represent a certain portion of the globe, or they must severely compromise on one or more of these characteristics: size, direction, or shape.  Here is a fun way to view different projections:

Projection file – a file with the extension .prj, which defines a coordinate reference system. Generally found as part of a shapefile.

Python – A widely-used (and easy to learn) open source programming language, which can be used in many GIS applications. For example, QGIS includes a Python “console” through which a user could progammatically manipulate spatial data.

Quantum GIS (QGIS) – A free, open-source, full-featured GIS software.

Open Source – A collaborative way of developing software in which the source code is publically available for anyone to view or work on. See FOSS.

Orthoimagery – Aerial photos that have been “orthorectified”.  This process adjusts for lense distortion to create a flat, planimetrically correct image. Often just called “aerial imagery”.

Raster – cell-based data, such as imagery or a digital elevation model, where each cell stores a discrete value.

Shapefile  a standard file format for vector data using the extension .shp, along with supporting files like .dbf, .shx, etc.

Spatial Data – Any dataset that includes, or is defined by, geographic coordinates, a.k.a. geospatial data.

TIGER/Line® – Publication of the US Census Bureau containing governmental boundaries, roads, census blocks and tracts, and demographic information.

USGS – US Geological Survey, creates and maintains many authoritative datasets, such as the National Elevation Dataset (NED) and the National Hydrology Dataset (NHD), as well as their popular (and iconic) topographical maps.

USDA – US Department of Agriculture, publishes (among other things) NAIP and NLCD (with NRCS).

US Census Bureau – Roads & streets, urban areas, census blocks

Vector Data – Spatial data stored in the form of individual geometries (i.e. “shapes”). Generally, shapes must be stored in separate files based on their shape type: point, line, or polygon.  Thus you may have a “point” shapefile to store address points and a “line” shapefile to store road alignments.

WGS84 – World Geodetic System 1984, datum developed in 1984 to model the entire world.  All world-wide datasets use this datum, and

WROC – Wisconsin Regional Orthography Consortium, good source for regional orthoimagery and LiDAR products.