# Essential Spatial Analyst terms

Term Description

Cell-based analysis

In cell-based analysis, each location is a value in a raster dataset, and the various tools generate an output raster based on applying some mathematical, spatial, or algorithmic rules to the input cell values.

Cell

A cell is the smallest unit of information in raster data. Each cell represents the numeric value of some measure at the corresponding unit area location on the earth. The various types of information the values can represent, and examples of each, are the following:

• Thematic data—Landuse, zoning
• Continuous information—Elevation, concentration surfaces
• Imaging pixels—Satellite images, aerial photographs

Cells are typically square in shape. The area each cell represents is dependent on the resolution of the raster. High-resolution (large-scale) raster cells would represent small areas, measured in units as small as square meters. The cells in a lower-resolution (small-scale) raster represent the uniform value of a larger area, such as hectares or square kilometers.

Cell values can also be used as an index with which other attribute values can be associated, such as soil type or vegetation class.

Map Algebra

Map Algebra is a semantic language that defines a syntax for applying mathematical and algorithmic operations on (generally) raster data to perform spatial analysis and create new raster datasets.

In general, Map Algebra has four main types of operations: local, focal, zonal, and global.

The general concepts behind Map Algebra originated with C. Dana Tomlin in Geographic Information Systems and Cartographic Modeling, Prentice Hall, 1990.

NoData

If there is either no information or insufficient information about the characteristics of the location a cell represents, that location is assigned a null value termed "NoData". Note that NoData and 0 are not the same—0 is a valid numerical value.

Raster

A spatial data model that defines space as an array of equally sized cells, arranged in rows and columns, and composed of single or multiple bands (layers). Each cell contains an attribute value. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are inherently contained in the ordering of the matrix. Groups of cells that share the same value represent the same type of geographic feature.

Spatial analysis

The process of examining the locations, attributes, and relationships of features in spatial data through overlay and other analytic techniques to address a question or gain useful knowledge. Spatial analysis extracts or creates new information from spatial data.

Spatial modeling

A methodology or set of analytic procedures used to derive information about spatial relationships between geographic phenomena.

It would also be helpful to be familiar with general imagery and raster terms.