Overview
Geospatial data is created, shared, and stored in many different formats. The two primary data types are raster and vector. Vector data is represented as either points, lines, or polygons. Discrete (or thematic) data is best represented as vector. Data that has an exact location, or hard boundaries are typically shown as vector data. Examples are county boundaries, the location of roads and railroads using lines, or point data indicating the location of fire hydrants.
By contrast, raster data is best suited for continuous data, or information that does not have hard boundaries or locations. As rasters, the data are viewed as a series of grid cells where each cell has a value representing the feature being observed. Think of raster data as appropriate for modeling surfaces like elevation, temperature, precipitation, or soil Ph. These phenomena are measured at intervals (think weather stations), and values in between are interpolated to create a continuous surface. Raster data also includes remote sensing imagery, like aerial photography and satellite imagery.
Vector Formats:
SHP: Shapefile
The ESRI Shapefile has become an industry standard geospatial data format, and is compatible to some extent with practically all recently released GIS software. To have a complete shapefile, you must have at least 3 files with the same prefix name and with the following extensions: .shp = shapefile, .shx = header and .dbf = associated database file. Additionally, you may have a .prj = Projection file, a .lyr = layer file, and other index files. All these files must be saved in the same workspace.
SDC: Smart Data Compression
SDC is ESRI's highly compressed format, which is directly readable by ArcGIS software.
GDB: Geodatabase
The file geodatabase is a collection of geographic datasets of various types, with the most basic types being vector, raster, and tabular data. There are three types of geodatabases: file, personal, and ArcSDE. Geodatabases are the native data format for ESRI's ArcGIS.
ArcInfo Coverage
An ArcInfo coverage has been phased out and is rarely seen/used today. It has largely been replaced by the geodatabase format. Coverages do not have an individual file extension. Instead it is composed of two folders within a "workspace" which each contain multiple files. One of the two folders carries the name of the coverage, and contains a number of various .adf files. The other folder is an "info" folder, which typically contains .dat and .nit files for all the coverages and grids in the workspace.
E00: Arc Export or Interchange Format
.e00 files are also rarely seen/used today, but are essentially ArcInfo Interchange or export files, used to conveniently copy and move ArcInfo GIS coverages (see above) and grids (see below). An .e00 file must be "imported" and converted in order to use the data in ArcGIS or other GIS software.
Raster Formats:
ArcInfo Grid
An ArcInfo Grid does not have an individual file extension. Instead it is composed of two folders within a "workspace" which each contain multiple files. One of the two folders carries the name of the grid, and contains a number of various .adf files. The other folder is an "info" folder, which typically contains .dat and .nit files for all the coverages and grids in the workspace.
Band Interleaved by Line (BIL), Band Interleaved by Pixel (BIP), and Band Sequential (BSQ).
BIL, BIP, and BSQ are formats produced by remote-sensing systems. The primary difference among them is the technique used to store brightness values captured simultaneously in each of several colors or spectral bands.
DEM (Digital Elevation Model)
DEM is a raster format used by the USGS to record elevation information. Unlike other raster file formats, DEM cells do not represent color brightness values, but rather the elevations of points on the earth’s surface.
GeoTIFF
As part of the header of the TIFF file, this provides the Lat/Long boundary extent of the data.
LiDAR
Light Detection and Ranging (LiDAR), is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. File formats vary by deliverable - but raw LiDAR point cloud data has a .LAS file extension. A DEM can be one deliverable from LiDAR.
