Glossary
Definitions for terms used throughout this guide. Distinctive terms also appear as hover tooltips wherever they occur in the documentation.
Interface architecture
These describe the layers of a dynamic datacube visualization, from the user's input down to the pixels on screen (see the visualization overview).
- User interaction
- The layer where the user interacts with the page to indicate what data and display options they want, through controls like time sliders, layer toggles, and zoom controls.
- Data orchestration
- Based on the user's selections, the logic that determines how to fetch data: API integration (such as STAC discovery) and coordination with backend services.
- Framework
- A visualization library that wraps a rendering engine with higher-level abstractions such as layer management, data binding, and interaction patterns. Examples include deck.gl and MapLibre.
- Rendering engine
- The engine that generates an image from input data, via a graphics context (WebGL, SVG, or DOM elements), drawing primitives, and coordinate systems.
Visualization
- Static visualization
- A visualization whose contents do not change after creation, like a map printed to paper.
- Dynamic visualization
- A visualization that responds to user input, such as zooming, panning, or changing the color scheme.
- Dynamic tiler
- A backend service that renders map tiles from source data on demand rather than from pre-rendered files. Examples include TiTiler and xpublish-tiles.
- Tile
- A small image (commonly 256×256 pixels) covering one region at one zoom level; the unit a web map fetches and draws.
- Zoom level
- An integer describing the resolution of a tiled map. Level 0 covers the whole world in a single tile, and each level adds detail by splitting every tile into four, doubling the resolution.
- Multiscales
- Precomputed downsampled copies of a dataset at multiple resolutions (a "pyramid"), so a viewer reads only the resolution it needs.
- Colormap
- A mapping from data values to colors, used to render numeric data as an image.
- CRS (coordinate reference system)
- A definition of how coordinates map to locations on Earth. Visualization often transforms between data, projected, and display coordinate reference systems.
- Web Mercator
- The map projection (EPSG:3857) used by most web map tiles.
- Range request
- An HTTP request for a byte range of a file, letting a client read part of a large file without downloading the whole thing.
Data and formats
- Datacube
- A multi-dimensional array of data, for example time × level × latitude × longitude × band, typically spanning 3 to 5 dimensions. See Data structures.
- Chunk
- A contiguous block of a chunked array, read and written as a unit. Chunk size strongly affects performance.
- Zarr
- A cloud-optimized format for chunked, compressed N-dimensional arrays.
- GeoZarr
- A geospatial convention layered on top of Zarr, covering multiscales and CRS encoding (EPSG, WKT2, or PROJJSON).
- COG (Cloud-Optimized GeoTIFF)
- A GeoTIFF structured for efficient range-request access on object storage.
- NetCDF
- A self-describing array format common in earth-science data.
- GRIB
- A binary format for gridded meteorological data.
- STAC (SpatioTemporal Asset Catalog)
- A JSON specification for describing and discovering geospatial datasets.
- OPeNDAP
- A protocol for remote access to subsets of scientific datasets over HTTP.
Data structures
Foundational concepts covered on the Data structures page.
- Index space
- The integer-indexed structure of an array. A value is addressed by its
position
(i, j[, k]); has no inherent units. See Data structures. - World space
- Where each value actually sits in a CRS — also "physical space" or "geographic space". Has units defined by the CRS (meters, degrees, …). See Data structures.
- Gridded
- Data tied to the cells (or nodes) of a grid; a value's location is implied by its index in the array. See Data structures.
- Ungridded
- Scattered or point observations that are not arranged on a grid; each value carries its own explicit coordinates. See Data structures.
- Structured grid
- A grid whose cells form a regular logical array addressable by integer indices, with connectivity implicit. Includes regular (rectilinear) and curvilinear grids. See Data structures.
- Unstructured grid
- A mesh whose cells are joined by an explicit connectivity list, with variable numbers of neighbors per node. See Data structures.
- DGGS (Discrete Global Grid System)
- A global tessellation of the sphere by a single cell family (often
equal-area), with hierarchical refinement and a specialized cell-ID
indexing scheme — connectivity is implicit in the ID arithmetic rather
than in
(i, j)array shape or an explicit connectivity list. Examples: HEALPix, H3, S2, cubed-sphere. See Data structures. - Regridding (resampling)
- The operation that moves data from one spatial sampling to another, for example from ungridded points onto a regular grid. Method matters: nearest, bilinear, and conservative each suit different quantities. See Data structures.
Satellite data products
Pointers to canonical external references for satellite Earth-observation product taxonomy. These terms are out of scope for an in-depth treatment here.
- Swath
- The strip of Earth's surface observed by a sensor as the platform moves along its orbit; the sensor's native acquisition geometry, indexed by along-track × across-track with 2-D geolocation arrays. Typical of Level-1/Level-2 products, distinct from a Level-3 product resampled onto a regular map grid. See Copernicus SentiWiki — Sentinel-1 products.
- Analysis-ready data (ARD)
- Any dataset that has been preprocessed such that it fulfills the quality standards required by the analysis to be performed on it. For satellite Earth observation specifically, CEOS-ARD (formerly CARD4L) is the community standard. See Stern et al., Frontiers in Climate (2021) — Pangeo Forge: Crowdsourcing Analysis-Ready, Cloud Optimized Data Production.
- Data processing levels
- A maturity ladder describing how far a product has been processed, from raw instrument data (Level 0) to model output (Level 4). The numbers are not portable across agencies — NASA, ESA/Copernicus, and USGS each define their own scheme. See NASA Earthdata — Data Processing Levels.
- Timeliness (NRT/STC/NTC)
- ESA's latency axis for a product: Near Real Time (hours), Short Time Critical, and Non Time Critical (best calibration accuracy). Independent of processing level. See Copernicus SentiWiki — Sentinel-3 products.