Introduction to GIS All materials by Austin Troy © 2003, except where noted Lecture 8: Site Selection and Suitability Analysis and Criterion- based mapping By Austin Troy, University of Vermont

Introduction to GIS All materials by Austin Troy © 2003, except where noted Cartographic Modeling Temporally static model that uses criteria to look for certain areas meeting or failing to meet given criteria Represents a given “snapshot in time” Site suitability, prioritization and selection models are examples of this

Introduction to GIS All materials by Austin Troy © 2003, except where noted Review of methods for site selection and suitability analysis Vector geoprocessing approach: –Combination of buffering, polygon overlay functions, spatial join (for assigning distances), attribute queries –Good for selecting geographic areas that meet or fail to meet criteria –Good for generating a few suitability classes

Introduction to GIS All materials by Austin Troy © 2003, except where noted Review of methods for site selection and suitability analysis Raster overlay methods: –Use map queries and map algebra between overlaying raster layers –Select individual pixels that meet or don’t meet criteria –Better for creating continuous indices, which can be made using map algebra –Especially good with distances and weighted distances as criteria

Introduction to GIS All materials by Austin Troy © 2003, except where noted Hybrid Methods Can combine raster and vector data queries by using zonal statistics or (in Arc View 3) Tabulate Areas.

Introduction to GIS All materials by Austin Troy © 2003, except where noted Hybrid Methods Can also convert between raster and vector to allow for multi-layer analysis in one format or the other

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions Topology This is another approach that is available only in Arc/Info workstation. It is a level of topology higher than polygon

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions Topology Allows for Nested representation: allows for hierarchical nesting of certain polygon types within larger polygon types Example: a regions layer may contain block groups within tracts within counties, within states, each level with their own behaviors and each with their own membership; The former Soviet Union through time

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions Topology Allows for Associations: dispersed or connected polygons can be given membership in the same feature; deals with “void area” Example: Hawaii or Florida; each comprised of many sub-features, but computer recognizes them as single entity

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions Topology Allows for Overlapping geographic features: features that are not spatially mutually exclusive, but overlap can be coded for Example: fire perimeters, overlapping soils or geologic data at different layers From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Fire perimeters over time

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions and Subclasses In Arc/Info a grouping of polygons that share some logical grouping are called a subclass Each hierarchical level is a subclass in this case From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions and Subclasses This allows attribute data to be stored much more efficiently. attributes can be associated with them which are distinct from the attributes associated with the individual polygons Region attributes are stored in subclass-level attribute tables that are named cover.PATregionsubclass (e.g. Census.PATcounty).

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions and Subclasses From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions and Subclasses In the upper one, the three islands are managed as a subclass In the lower, 103, 104 and 105 refer to areas of fire damage for three given years, each managed as a subclass From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Regions and Subclasses Once you’ve created regions, you can run any geoprocessing techniques we’ve learned, such as intersect, clip, union and identity using subclasses as inputs instead of polygon layers For instance, in my fire perimeter layer, maybe I have a subclass for early twentieth century fire perimeters, and one for later 20 th century perimeters. From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Methods for Making Regions AREAQUERYa dynamic polygon overlay tool that allows you to integrate, query, and aggregate polygon and region layers from multiple coverages in a single operation. POLYREGIONconverts a polygon coverage to a region subclass. All polygons in the in_cover become a region of the output subclass. REGIONBUFFER creates buffer regions around specified input coverage features. REGIONCLASScreates preliminary regions from arcs by region subclass, or appends preliminary regions to existing regions for the subclass. REGIONCLEAN merges adjacent polygons that belong to the same regions. REGIONDISSOLVE constructs new region subclasses by aggregating polygons or regions with the same value for a specified item. REGIONJOIN creates new regions by joining a related table to a region subclass attribute table. REGIONQUERY creates new regions from existing regions or polygons based on attribute values in multiple subclasses and specified output items. REGIONXTAB an ATOOL enabling you to do region cross tabulation. In ARCEDIT MAKEREGIONcreates regions from selected polygons. From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Example: Areaquery This is an extremely helpful tool for doing multi-layer queries with a minimum of steps Utilizes the regions approach for analysis, querying and manipulation of overlapping coverages Areaquery’s power lies in its ability to integrate many coverages (up to 32) into one “super-coverage” so all the coverages can be analyzed Can do queries for highly specific criteria, and on numerous attributes Similar to doing multiple unions, but simpler and more data efficient

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery Each polygon input layer becomes like a region subclass Can aggregate multiple polygon and region layers from different coverages into one output subclass When associate a subclass with an input cover, each polygon in that input cover becomes a region in the specified region subclass Areaquery selects and dissolves regions from all region subclasses. It lets you select overlap conditions between overlapping regions, covert noncontiniguous regions to contiguous ones and vice versa

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery Say you want to do a specific query for the following: –landtype is brushland, soil is suitable for development, site within 300 meters of sewer line, site is 20 meters beyond existing streams and the site must contain a contiguous area of 8000 square meters First, you specify each coverage to be analyzed; in the process, each polygon coverage is turned into a regions cover Then you specify a logical query across data sets

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example Say we’re doing a site selection where: preferred landuse is brushland Soil types should be suitable for development Site must be within 300 meters of existing sewer lines Site must be beyond 20 meters of existing streams Site must contain an area of at least 8000 meters square These codes are specific to the coverages in our database: –LANDUSE (attribute LU-CODE = brushland) –SOILS (attribute SUIT >= 2 - suitable for development), –SEWERBUF (a 300 meter buffer around sewerlines) –STREAMBUF (a 20 meter buffer around streams). From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery From ESRI ‘s ArcINFO help

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example Now let’s say we wanted to try this on our habitat site selection example we did in lab We would start by turning all our buffer feature classes into coverages in Arc Catalog

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example Then input expression Followed by the coverage names and subclass names

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example Followed by your logical expression, which here is just presence/absense

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery results You get a coverage with a bunch of subclass, one for your desired conditions, and one for each constituent subclass Hence, this becomes like an Arc/Info version of a geodatabase

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery results Here’s land meeting all our criteria

Introduction to GIS All materials by Austin Troy © 2003, except where noted One more example Now let’s say we’re looking for vacant land (LUcode=3100) that is in a floodplain (not $FLOOD) and not on public land (not $open), so that the government can target areas to buy to prevent future floodplain development

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example 2 Again we specify our function and then our subclasses Then our criteria

Introduction to GIS All materials by Austin Troy © 2003, except where noted Areaquery example 2 Then we get the following result