Slide 1

Overlay A series of registered data layers overlaying each other Arguably the most important GIS analysis function Slide 2 Overlay Derived from manual cartographic overlay using Mylar sheets (transparent plastic) that were physically overlaid on top of one another. -Ian McHarg in landscape architecture at University of PA Slide 3 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 on polygon More complex in vector than in raster Slide 4 Overlay Raster overlay layers are registered layers have same resolution Slide 5 Overlay Point in polygon: raster Where are there trees in the urban area? 0 10 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 1 2 22 0 0 2 2 2 0 2 2 2 2 2 2 0 0 0 2 2 0 0 0 2 2 0 - not a tree 1 - tree PointPolygon 0 - not urban 2 - urban 0 - not urban, no tree 1 - not urban, tree 2 - urban, no tree 3 - urban, tree 2 32 0 1 2 2 2 0 2 2 2 2 2 2 0 0 1 2 2 0 0 0 3 3 += Result Slide 6 Overlay Point in polygon: raster Where are there trees in the urban area? 0 - not urban, no tree 1 - not urban, tree 2 - urban, no tree 3 - urban, tree 2 32 0 1 2 2 2 0 2 2 2 2 2 2 0 0 1 2 2 0 0 0 3 3 reclassify < 3 = 0 3 = 1 0 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 - not an urban tree 1 - urban tree Slide 7 Overlay 0 11 0 0 1 1 1 1 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 2 22 0 0 2 2 2 0 2 2 2 2 2 2 0 0 0 2 2 0 0 0 2 2 0 - not a road 1 - road LinePolygon 0 - not urban 2 - urban 0 - not urban, no road 1 - not urban, road 2 - urban, no road 3 - urban, road 2 33 0 0 3 3 3 1 2 2 3 2 2 2 1 0 0 2 2 1 0 0 2 2 += Result Line in polygon: raster Where are there roads in the urban area? Slide 8 Overlay Point in polygon: vector Jacobsen plumbline algorithm Pass a line through the point and polygon if number of line/polygon intersections is: even - point is outside odd - point is inside Slide 9 Overlay Point in polygon: vector result must include attribute information A B C ID Tree A Elm B Maple C Elm Point Table ID Tree Cover A Elm Rural B Maple Rural C Elm Urban Point Table ID Cover 1 Rural 2 Urban Poly Table 12 + A B C= Input Output Slide 10 Overlay Line in polygon: vector result must include attribute information A B C ID Street A Race B Race C Arch Point Table ID Street Cover A Race Rural B Race Urban C Arch Urban D Race Urban Point Table ID Cover 1 Rural 2 Urban Poly Table 12 += Input Output A B C 12 D Slide 11 Overlay Raster overlay Boolean combination Slide 12 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? Agriculture 0 00 1 1 0 0 1 1 0 0 0 1 1 0 0 0 0 1 1 0 0 0 1 1 Poor soil quality 1 00 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 Agr and poor soil 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 1 Slide 13 Overlay Raster overlay Slide 14 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? 1 11 2 2 1 1 2 2 1 1 1 2 2 1 0 0 0 2 2 0 0 0 2 2 0 11 2 2 0 0 2 2 0 0 1 1 1 0 1 0 1 0 0 1 0 0 0 0 0 - residential 1 - forest 2 - agriculture Land coverSoil quality 0 - poor 1 - fair 2 - good += Output agriculture + poor = 2 forest + fair = 2 residential + good = 2 Slide 15 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? 1 11 2 2 1 1 2 2 1 1 1 2 2 1 0 0 0 2 2 0 0 0 2 2 0 - residential 1 - forest 2 - agriculture Land coverAgriculture 0 00 1 1 0 0 1 1 0 0 0 1 1 0 0 0 0 1 1 0 0 0 1 1 reclassify 0 - not agriculture 1 - agriculture Slide 16 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? 0 - not poor 1 - poor Soil qualityPoor soil quality 1 00 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 reclassify 0 11 2 2 0 0 2 2 0 0 1 1 1 0 1 0 1 0 0 1 0 0 0 0 0 - poor 1 - fair 2 - good Slide 17 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? += Output Agriculture 0 00 1 1 0 0 1 1 0 0 0 1 1 0 0 0 0 1 1 0 0 0 1 1 0 - not agriculture 1 - agriculture 0 - not poor 1 - poor Poor soil quality 1 00 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 1 00 1 1 1 1 1 1 1 1 0 1 1 1 0 1 0 2 2 0 1 1 2 2 0 - not agr., not poor 1 - agr., not poor or not agr, poor 2 - agr, poor Slide 18 Overlay Raster overlay: polygon on polygon where is agriculture on poor quality soil? Output 1 00 1 1 1 1 1 1 1 1 0 1 1 1 0 1 0 2 2 0 1 1 2 2 0 - not agr., not poor 1 - agr., not poor or not agr, poor 2 - agr, poor Final Output 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 - not agr. on poor soil 1 - agr. on poor soil reclassify Slide 19 Overlay Raster overlay: map algebra += Hot + Humid Index Daily high temperature 0 10 1 1 0 1 2 2 0 1 2 2 2 1 1 0 1 1 2 1 1 1 2 2 0 - mild 1 - warm 2 - hot 0 - not humid 1 - semi humid 2 - very humid Daily high humidity 0 12 2 2 0 1 2 2 1 0 1 2 2 0 0 1 1 0 0 0 0 0 1 1 0 22 3 3 0 2 4 4 1 1 3 4 4 1 1 1 2 1 2 1 1 1 3 3 0 - very low 1 - low 2 - medium 3 - high 4 - very high Slide 20 Overlay Raster overlay: map algebra can use addition, multiplication, etc. can weight certain data layers can use any number of data layers cant 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 Slide 21 Overlay Vector topologic overlay: Boolean operators Intersection (and)Union (or) Identity Slide 22 Overlay Vector topologic overlay: intersection Slide 23 Overlay Vector topologic overlay: intersection (and) Agriculture A B A Good Quality Soil ID Owner A Brown B Smith ID Quality A good B good B Area of intersection New node Build new topology Slide 24 Overlay Vector topologic overlay: intersection (or) Output ID Owner Quality A Brown good B Smith good A B Area of intersection New node Build new topology Slide 25 Overlay Vector topologic overlay: union Agriculture A B A Good Quality Soil ID Owner A Brown B Smith ID Quality A good B good B Area of union New node Build new topology Slide 26 Overlay Vector topologic overlay: union Area of union New node Build new topology Output ID Owner Quality A good B Brown good C Brown D Smith E Smith good A BC DE Slide 27 Vector topologic overlay: identity Agriculture (input layer) A B A Good Quality Soil (identity layer) ID Owner A Brown B Smith ID Quality A good B good B Area of identity New node Build new topology Slide 28 Overlay Vector topologic overlay: identity Area of identity New node Build new topology Output ID Owner Quality A Brown good B Brown C Smith D Smith good AB CD