Analytical GIS Capabilities There are many ways to classify the analytic functions of a GIS. The classification used for this lecture makes the following distinctions in function classes: Measurement and classification functions Overlay functions Neighbourhood functions Connectivity functions

Spatial selection queries Spatial selection by attribute conditions

Classification Line Dissolve (Map Dissolve) 2 3 1 2 1 4 1 grain crops 2 orchards 3 residential 4 commercial 1 agricultural 2 non-agricultural

Overlay Functions These functions (Operators) are as follows: polygon intersection spatial join polygon clipping polygon overwrite

Overlay A series of registered data layers ‘overlaying’ each other Arguably the most important GIS analysis function

Overlay An overlay operation takes two or more data layers as input and results in an output data layer Three types of overlay: Point in polygon Line in polygon Polygon (polygon on polygon)

Point in Polygon Overlay Trees Land Cover NewTrees 1 2 A A C + = C B B Point Table Poly Table Point Table ID Tree A Elm B Maple C Elm ID Cover 1 Rural 2 Urban ID Tree Cover A Elm Rural B Maple Rural C Elm Urban

Line in Polygon Overlay Streets Land Cover NewStreets C C A A + = D B B 1 2 Line Table Poly Table Line Table ID Street A Race B Race C Arch ID Cover 1 Rural 2 Urban ID Street Cover A Race Rural B Race Urban C Arch Urban D Race Urban

Polygon Overlay Intersection (and) Union (or) Identity

Polygon Overlay: Intersection Agriculture Land Cover <Intermediate> A A B B ID Owner A Brown B Smith ID Cover A commercial B industrial Area of intersection New node

Polygon Overlay: Intersection <Intermediate> Output A B ID Owner Cover A Brown commercial B Smith industrial Area of intersection New node

Polygon Overlay: Union Agriculture Land Cover <Intermediate> A A B B ID Owner A Brown B Smith ID Cover A commercial B industrial Area of union New node

Polygon Overlay: Union Output <Intermediate> B C A D E ID Owner Cover A commercial B Brown commercial C Brown D Smith E Smith industrial Area of union New node

Polygon Overlay: Identity Agriculture (input layer) Land Cover (identity layer) <Intermediate> A A B B ID Owner A Brown B Smith ID Cover A commercial B industrial Area of identity New node

Polygon Overlay: Identity Output <Intermediate> A B C D ID Owner Cover A Brown commercial B Brown C Smith D Smith industrial Area of identity New node

Raster Overlay GISs that support raster processing - as do most -usually have a full language to express operations on rasters.

Neighborhood functions To perform neighborhood analysis, we must: state which target locations are of interest to us, and what is their spatial extent, define how to determine the neighborhood for each target, define which characteristic(s) must be computed for each neighborhood.

Neighbourhood functions Proximity computation: Buffer zone generation Thiessen polygon generation

Neighbourhood functions

Buffer Definition of what is within/without a given proximity Line buffer Point buffer Polygon buffer

Doughnut Buffer e.g. within 10 meters but not within 5 meters Buffer polygon 5 10 ‘Hole’

Variable Buffer Buffer distance varies by some feature attribute or friction surface

Variable Buffer ID Dist A 3 B 2 C 5 B A Original line C 4 6 10 Buffer polygon

Neighbourhood functions

Unit Demand (l/day/ha) Table 12.3 Computing water use based on land-use area  Node Total Node Area (ha) Land Use Type Land Use Area (ha) Unit Demand (l/day/ha) Demand (l/day) Node Total (l/day) J-1 6.88 Industrial 11,200 77,100 J-2 7.69 Industrial Commercial Residential 1.38 0.92 5.38 11,200 4,700 7,500 15,500 4,300 40,400 60,200 J-3 Commercial Residential Undeveloped 1.31 5.15 1.23 4,700 7,500 0 6,100 38,600 0 44,800 J-4 8.50 Industrial Commercial Residential Undeveloped 0.17 0.10 2.45 5.78 11,200 4,700 7,500 0 1,900 470 18,400 0 20,800 J-5 8.09 Industrial Commercial 6.48 1.62 11,200 4,700 72,500 7,600 80,100 J-6 4.86 0.20 1.36 3.30 2,200 6,400 24,800 33,400