GUS: 0262 Fundamentals of GIS Lecture Presentation 7: Raster Operations Jeremy Mennis Department of Geography and Urban Studies Temple University

Map Algebra and Cartographic Modeling A raster modeling language, and an approach to GIS analysis design, developed by J.K. Berry and C. Dana Tomlin in the late 1970s - early 1980s. It now forms the basis for grid-based analysis in ArcInfo (GRID and Spatial Analyst) and other GIS packages.

Cartographic Modeling The representation of a geographic domain through a set of raster data layers. Tools for manipulating and transforming those data layers (map algebra). Conventions for designing and documenting models that integrate and relate various data layers. Structures to provide program control in the development of those models.

Map Algebra A set of formally defined manipulations on raster data. Operations: Fundamental mathematical and logical operations on raster data Functions: Complex combinations of operations

Functions: Types Higher order data manipulations on raster grids built from the more basic operators. Local: compute on single-cell basis Focal: compute on a neighborhood Zonal: use zones derived from a separate grid for evaluation

Functions: Local – Multiple Values

Functions: Local - Mean

Functions: Focal – Immediate Neighborhood

Functions: Focal – Majority Min Mean

Functions: Zonal – Entire Zones

Functions: Zonal - Max

Classification Raster reclassification: land cover grain crops 2 orchards 3 residential 4 commercial 1 agricultural 2 non-agricultural

Classification Raster reclassification: temperature (interval) Grid cell value = temperature (F)

Buffer raster surface of within/not within proximity Spread operation from buffered feature (0) Reclassify: 1 within 1 unit 0 not within 1 unit

Raster Overlay += Hot + Humid Index Daily high temperature mild 1 - warm 2 - hot 0 - not humid 1 - semi humid 2 - very humid Daily high humidity very low 1 - low 2 - medium 3 - high 4 - very high

Raster Overlay –can use addition, multiplication, etc. –can ‘weight’ certain data layers –can use any number of data layers –can’t use nominal data unless it used as inclusionary/exclusionary by reclassification! –Be careful with ordinal data - classification impacts the results of overlay! –Standardize interval/ratio data

Program Control: Statements and Programs Statement: notation to represent operations and functions e.g. NEWLAYER = LocalFUNCTION of FIRSTLAYER and SECONDLAYER Program: notation to represent a procedure; i.e. a sequence of statements in which each statement operates on the result of a previous statement

Program Control: Programs

Cartographic Modeling in ArcInfo: ModelBuilder Locating Suitable Sites for a Waste Dump

Cartographic Modeling in ArcInfo: ModelBuilder