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Geospatial & Earth Observation Glossary
This glossary provides definitions for common terms used in geospatial data science and Earth observation. Understanding these terms is essential for working with spatial data and communicating effectively with collaborators.
Spatial Data Fundamentals
Raster Data
Data represented as a regular grid of cells (pixels), where each cell holds a numerical value. Used for continuous phenomena like elevation, temperature, or satellite imagery.
Vector Data
Data represented as discrete geometric features — points, lines, and polygons — with associated attribute tables. Used for discrete features like buildings, roads, and administrative boundaries.
Coordinate Reference System (CRS)
A system that defines how coordinates (numbers) relate to positions on the Earth's surface. Includes a datum (model of the Earth's shape), a projection (how the 3D surface is flattened to 2D), and a coordinate system (units and axes).
EPSG Code
A standardized numerical identifier for coordinate reference systems, maintained by the IOGP. Example: EPSG:4326 = WGS 84 (latitude/longitude).
Projection
A mathematical transformation that converts 3D coordinates on the Earth's surface to 2D coordinates on a flat map. All projections introduce some distortion (area, shape, distance, or direction).
Datum
A mathematical model of the Earth's shape used as a reference surface. Common datums: WGS 84 (global, GPS), ETRS89 (Europe).
Georeferencing
The process of assigning real-world coordinates to data (an image, a map, a dataset) so it can be placed correctly on the Earth's surface.
Remote Sensing Terms
Remote Sensing
The acquisition of information about objects or phenomena from a distance, typically using sensors on satellites or aircraft.
Multispectral Imagery
Imagery captured in multiple discrete wavelength bands (typically 4-12 bands), such as blue, green, red, and near-infrared.
Hyperspectral Imagery
Imagery captured in many narrow, contiguous wavelength bands (typically 100-300+), providing a near-continuous spectrum for each pixel.
Spatial Resolution
The size of a single pixel on the ground. A 10 m resolution means each pixel covers a 10 × 10 m area. Finer resolution = more detail but larger file sizes.
Temporal Resolution
How frequently a sensor revisits the same location. Sentinel-2 has a 5-day revisit time at the equator.
Spectral Resolution
The number and width of wavelength bands a sensor records. More and narrower bands = finer spectral detail.
Radiometric Resolution
The sensitivity of a sensor to differences in energy, typically expressed in bits (e.g., 12-bit = 4096 levels).
NDVI (Normalized Difference Vegetation Index)
A spectral index calculated as (NIR - Red) / (NIR + Red) that indicates vegetation health and density. Values range from -1 to +1, with healthy vegetation typically above 0.3.
Atmospheric Correction
The process of removing atmospheric effects (scattering, absorption) from satellite imagery to obtain surface reflectance values.
Orthorectification
The correction of geometric distortions in aerial or satellite imagery caused by terrain relief and sensor geometry, producing a geometrically accurate map-like product.
GIS and Analysis Terms
GIS (Geographic Information System)
A system for capturing, storing, analyzing, and visualizing spatial data and its associated attributes.
Spatial Join
An operation that transfers attributes from one layer to another based on their spatial relationship (e.g., points falling within polygons).
Buffer
A zone of specified distance created around a geographic feature. Used for proximity analysis (e.g., 500 m buffer around a school).
Overlay
A set of operations (intersection, union, difference) that combine two spatial layers to produce new features.
Geocoding
The process of converting addresses or place names into geographic coordinates (latitude/longitude).
Spatial Autocorrelation
The degree to which values at nearby locations are similar. Measured by statistics like Moran's I.
Zonal Statistics
The calculation of statistics (mean, sum, count, etc.) for raster cell values within vector polygon zones.
Data and Format Terms
GeoTIFF
A TIFF image format extended with embedded georeferencing metadata (CRS, extent, resolution).
Cloud Optimized GeoTIFF (COG)
A GeoTIFF with internal tiling and overviews optimized for efficient partial reads over HTTP.
Shapefile
A legacy multi-file vector format (.shp, .shx, .dbf, .prj) from ESRI. Being replaced by GeoPackage.
GeoPackage
An open, SQLite-based container for vector and raster geospatial data. The modern replacement for Shapefiles.
NetCDF
Network Common Data Form — a self-describing format for array-oriented scientific data, widely used in climate science.
STAC (SpatioTemporal Asset Catalog)
A JSON-based specification for describing and cataloging geospatial assets for search and discovery.
WMS / WFS / WCS
OGC web service standards for serving map images (WMS), vector features (WFS), and raster coverages (WCS) over the internet.
Point Cloud
A collection of 3D points (X, Y, Z) representing the external surface of objects, typically acquired by LiDAR or photogrammetry.
DEM (Digital Elevation Model)
A raster representation of terrain elevation. Related: DSM (Digital Surface Model) includes buildings and vegetation; DTM (Digital Terrain Model) represents bare earth.
Need clarification on a term? Contact us at rdhub@mdsi.tum.de or explore our Use Cases for practical examples.