Raster is a data format consisting of regular grids of values, usually stored in an image-like format.
What is raster data?
Raster data consists of spatial features or phenomena that are partitioned into reguar sampling units called "cells" (grid cells) and organized into a Cartesian matrix.
Cell values signify the presence or absence of the categorical phenomena, or the values of continuous phenomena (e.g. topography, temperature, etc.)
Raster data share many characteristics with photographs, as values are often measurements across the surface of the earth. Raster data are common for remote sensed products, where cameras allow capturing gridded data at regular intervals. Raster data are also the most common source of elevation data.
Raster data vs. Vector data:
In the concept of GIS, there are two primary data types:raster and vector. Vector data consists of points, lines and polygons, while raster data consists of a "fishnet overlay" of cells that create association with each other by having similar cell values.
- Good for complex analysis
- Efficent for overlays
- Data structure common for imagery
- Compact data structure (generally smaller files than raster data)
- Efficient for topological operations (examining the relationship of two features in close proximity)
- True representation of shape
Common raster data file formats utilized in GIS:
ADRG - National Geospatial-Intelligence Agency (NGA)'s ARC Digitized Raster Graphics
BIL - Band Interleaved by Line (image format linked with satellite derived imagery)
CADRG - National Geospatial-Intelligence Agency (NGA)'s Compressed ARC Digitised Raster Graphics (nominal compression of 55:1 over ADRG)
CIB - National Geospatial-Intelligence Agency (NGA)'s Controlled Image Base (type of Raster Product Format)
Digital raster graphic (DRG) - digital scan of a paper USGS topographic map
ECRG - National Geospatial-Intelligence Agency (NGA)'s Enhanced Compressed ARC Raster Graphics (Better resolution than CADRG and no color loss)
ECW - Enhanced Compressed Wavelet (from ERDAS). A compressed wavelet format, often lossy.
ESRI GRID - proprietary binary and metadataless ASCII raster formats used by Esri
GeoTIFF - TIFF variant enriched with GIS relevant metadata
IMG - ERDAS IMAGINE image file format
JPEG2000 - Open-source raster format. A compressed format, allows both lossy and lossless compression.
MrSID - Multi-Resolution Seamless Image Database (by Lizardtech). A compressed wavelet format, allows both lossy and lossless compression.
netCDF-CF - netCDF file format with CF medata conventions for earth science data. Binary storage in open format with optional compression. Allows for direct web-access of subsets/aggregations of maps through OPeNDAP protocol.