Glossary.

Plain-language definitions for 55+ key terms in space-domain geographic information systems. Use this page as a reference while working through the course.

WGS84

World Geodetic System 1984. The geodetic datum used by GPS and most satellite-derived coordinates. EPSG:4326 is its geographic (lat/lon) form.

EPSG

European Petroleum Survey Group code — a registry of coordinate reference system identifiers. EPSG:4326 = WGS84 lat/lon. EPSG:3857 = Web Mercator.

Ellipsoid

A geometric approximation of Earth's shape: bulged at the equator, flattened at the poles. WGS84 ellipsoid: equatorial radius 6378137 m, flattening 1/298.257223563.

Geoid

The equipotential surface of Earth's gravity field that best matches mean sea level. Differs from the ellipsoid by up to plus or minus 100 m globally.

EGM2008

Earth Gravitational Model 2008. The standard global geoid model published by NGA, accurate to about 15 cm.

Mercator (Web Mercator)

EPSG:3857. The conformal projection used by Google Maps, Mapbox, and most slippy web maps. Distorts area near the poles.

UTM

Universal Transverse Mercator. Earth divided into 60 6-degree-wide zones. Conformal and nearly equidistant within a zone. Cape Canaveral is UTM Zone 17N (EPSG:32617).

Equirectangular

Plate carree projection where latitude and longitude map directly to y and x. Cheap, common for global imagery. Distorts near the poles.

MGRS

Military Grid Reference System. NATO-standard coordinate notation using a global grid with variable precision (km to m).

Vector data

GIS data representing the world as discrete geometric objects (points, lines, polygons) with attributes. GeoJSON is the most common format.

Raster data

GIS data as a grid of cells, each holding a value. Satellite imagery is raster. GeoTIFF is the standard format.

GeoJSON

An open standard format for encoding geographic features in JSON. Used universally on the web.

GeoTIFF

A TIFF image with embedded georeferencing metadata. The standard raster format in GIS.

COG

Cloud-Optimized GeoTIFF. A regular GeoTIFF organized so HTTP-range-request access fetches just the needed bytes without downloading the whole file.

Zarr

A format for chunked, compressed, multi-dimensional arrays. Standard for cloud-native gridded data (climate reanalysis, time series).

STAC

SpatioTemporal Asset Catalog. A spec for cataloging geospatial assets with searchable APIs. Major STAC catalogs: Microsoft Planetary Computer, AWS Earth Search.

PostGIS

The spatial extension to PostgreSQL. Adds geometry and geography types, hundreds of ST_ functions, GIST spatial indexes.

GIST index

A PostgreSQL index type using an R-tree for spatial queries. Essential for performance on PostGIS geometry columns.

Spatial join

An operation that attaches attributes from one layer to another based on a spatial relationship (within, intersects, etc.) rather than a key match.

TLE

Two-Line Element set. NORAD's plain-text format encoding a satellite's Keplerian orbital elements plus drag and perturbation terms in 70 characters per line. Distributed by Space-Track.org and CelesTrak.

SGP4

Simplified General Perturbations 4. The standard orbital propagation algorithm for use with TLEs. Accurate to about 1 km for a fresh TLE.

Keplerian elements

The six orbital parameters that uniquely describe an orbit shape and orientation: semi-major axis, eccentricity, inclination, RAAN, argument of periapsis, true anomaly.

Ground track

The path on Earth's surface traced by the sub-satellite point of a satellite over time.

Sub-satellite point

The point on Earth's surface directly below a satellite.

LEO

Low Earth Orbit, under 2000 km. ISS, Starlink, Hubble, Landsat, Sentinel-2 all operate here.

MEO

Medium Earth Orbit, 2000 to 35786 km. GPS, GLONASS, Galileo operate here.

GEO

Geostationary Orbit, 35786 km altitude over the equator. GOES, Himawari, most communications satellites.

Sun-synchronous orbit

A nearly polar orbit at about 98-degree inclination where the satellite passes the equator at the same local solar time each orbit. Used for Earth observation.

ABI

Advanced Baseline Imager. The primary instrument on GOES-R series satellites. 16 spectral bands from visible to longwave IR.

GOES-R

NOAA's geostationary weather satellite series. GOES-18 (West, 137.0W) and GOES-19 (East, 75.2W) are the operational satellites.

Himawari-9

JMA's geostationary weather satellite at 140.7E. Covers East Asia and the western Pacific.

Band 7

GOES-R ABI Band 7 at 3.9 micrometers — the mid-wave infrared band used for thermal hotspot detection, including rocket plumes and wildfires.

Brightness temperature

Temperature of a perfect black body that would emit the observed radiance. Computed via the inverse Planck function. Standard unit for thermal IR analysis.

NDVI

Normalized Difference Vegetation Index, computed as (NIR - Red) / (NIR + Red). High for healthy vegetation, low for bare soil.

SAR

Synthetic Aperture Radar. Active microwave imaging that sees through clouds and works day or night. Sentinel-1 is the workhorse civilian C-band SAR.

InSAR

Interferometric SAR. Phase-difference analysis between two SAR acquisitions, capable of measuring ground deformation to the millimeter.

Parallax in remote sensing

Apparent shift of a high-altitude feature (e.g. rocket plume at 50 km) as seen from a satellite, compared to its true ground position. Must be corrected for accurate geolocation.

CesiumJS

The open-source 3D globe library. Industry standard for serious web-based 3D GIS.

MapLibre GL JS

The community fork of Mapbox GL JS. WebGL-based vector tile renderer for web maps.

Vector tiles

Pre-indexed pyramid of small geographic data tiles served as Protocol Buffers. Smaller, smoother, and more flexible than raster tiles.

PMTiles

A single-file alternative to MBTiles that can be served directly from S3 via HTTP range requests — no tile server needed.

ITAR

International Traffic in Arms Regulations. US law controlling export of defense-related articles and services, including some satellite imagery.

NOTAM

Notice to Air Missions (FAA). Pre-launch safety advisory defining airspace exclusion for launches.

FIRMS

Fire Information for Resource Management System. NASA's near-real-time wildfire hotspot data, used to filter out fire false-positives in plume detection.

AIS

Automatic Identification System. Maritime vessel tracking transmitted on VHF and aggregated globally.

ADS-B

Automatic Dependent Surveillance-Broadcast. Aircraft transponder data broadcasting position and identity.

ʻĀina

Hawaiian for land — more specifically, that which feeds and sustains. In Hawaiian thought, place is not a passive backdrop but a living relative. ʻĀina-based mapping (used in Hawaiʻi by community organizations) puts the well-being of the land at the center of the question, not just at the legend.

Ahupuaʻa

Traditional Hawaiian land division running from mauka (mountain) to makai (sea), encompassing a complete watershed and the social/ecological unit organized around it. Used as a planning unit in modern Hawaiʻi for restoration, fisheries, and water management.

Kuleana

Hawaiian for responsibility — particularly the responsibility one has by virtue of relationship to a place, a people, or a tradition. Often invoked in conversations about how to use powerful tools (satellite imagery, GIS, data) ethically.

Wayfinding

The Pacific tradition of long-distance ocean navigation using stars, swells, bird flight, and other natural signs — preserved and revived through the Polynesian Voyaging Society and the canoe Hōkūleʻa. A complete coordinate system that operated for millennia without instruments.

Hōkūleʻa

The Polynesian Voyaging Society's double-hulled voyaging canoe, sailed since 1976 to reawaken traditional Pacific navigation. Has completed multi-year worldwide voyages using traditional wayfinding alongside modern safety systems.

Mauka / Makai

Hawaiian directional pair meaning 'toward the mountain' and 'toward the sea.' A coordinate system rooted in place rather than abstract compass directions — Hawaiian addresses and conversations often use this pair instead of N/S/E/W.

Mauna Kea

The 4,205-meter summit on the island of Hawaiʻi sacred to Native Hawaiian tradition; also home to several major astronomical observatories. The site of important ongoing conversations about science, sacredness, and stewardship.

Kīlauea

Active shield volcano on the island of Hawaiʻi, monitored intensively by the USGS Hawaiian Volcano Observatory. The 2018 lower East Rift Zone eruption was tracked extensively via satellite thermal IR (the same Band 7 LaunchDetect uses) and InSAR.

Indigenous data sovereignty

The principle that data about Indigenous peoples and places belongs to those peoples — not to whoever collected it. A growing field shaping geospatial work in Hawaiʻi, Aotearoa, and across Native communities; informs decisions about what to publish openly and what to keep within community.