## GIS

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# Map Algebra

Map Algebra
map algebra - [data analysis] A language that defines a syntax for combining map themes by applying mathematical operations and analytical functions to create new map themes.

Map Algebra
From now on we will assume all grids have been resampled if necessary to the same cell size and mesh. By "mesh" we mean simply the set of coordinates of cell boundaries. A grid with a cell size of 10 may have a mesh in the X-direction of {..., -10, 0, 10, 20, ...

Map Algebra
For most grid functions, other than those which simply identify a selected group of cells, operations take the conceptual format of an algebraic expression. For this reason, the syntax of grid analytical operations is often referred to as "map algebra.

Map Algebra
The premise for this concept follows that since digital data can be assigned a value, mathematical algorithms can manipulate it. For example, (Map #1 + Map #2) / (Map #3 * Map #4). This is one of the basic foundations of an analytical GIS. Maps have VALUE.

map algebra,
terrain analysis,
hydrologic modeling,
network analysis,
comprehensive searchable toolbox of functions,
define and run reusable analysis routines by chaining functions using a graphical modelling tool,
and many others.

Map algebra - A suite of arithmetical operations (i.e. addition, subtraction, multiplication and division) and their combinations for manipulating and analyzing raster data.

Mapjoin - The process of physically joining digital map files into a larger map or a Seamless geographic database.

This 'map algebra' is similar to traditional algebra where basic operations, such as addition, subtraction and exponentiation, are logically sequenced for specific variables to form equations-however, ...

A little Map Algebra
We now have the information we need about slope and accessibility for each location in our study area.

2.5.1 Python Map Algebra in 10.0
3 Python and GDAL
3.1 Installing the GDAL bindings
3.2 Pre-packaged python+GDAL bundles ...

Raster map algebra and aggregation
The r.mapcalc command provides raster map algebra methods. The r.average command aggregates one map based on a second map.
Raster map resampling and interpolation methods
GRASS offers various raster resampling and interpolation methods: ...

* Map algebra(5) may be used to manipulate model data layers. This allows a model layer's cells to be set to a number or some function of another data layerwhich permits the rapid evaluation of management scenarios that would otherwise be monumental undertakings.

Raster overlay, frequently called map algebra, is based on calculations which include arithmetic expressions and set and Boolean algebraic operators to process the input layers to create an output layer.

In raster data analysis, the overlay of data sets is accomplished through a process known as "local operation on multiple rasters" or "map algebra," through a function that combines the values of each raster's matrix.

GRID A fully integrated grid (cell-based) geoprocessing system for use with ArcInfo. GRID supports a Map Algebra spatial language that allows sophisticated spatial modeling and analysis.

See also: What is the meaning of Map, Model, GIS, Analysis, Geographic?

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