GIS in the Social and Natural Sciences. Last Lecture. Today s Outline 5/14/2017. GEOG 4110/5100 Special Topics in Geography

Transcription

1 GEOG 4110/5100 Special Topics in Geography GIS in the Social and Natural Sciences Working with Vector Data in a GIS Last Lecture We talked about the main types of vector data models (CDS, TDS, TIN, Networks) What topology means and why it is important How to work with topologic and nontopologic data To be critical about the need for topology Today s Outline We will talk about some vector operations basis for spatial data analysis Measurements Selection Classification & Dissolve uffering and spatial Overlay in general 1

2 Learning Objectives Understanding spatial data analysis in vector data Learning about vector operations Fundamental concepts measurements, buffers, overlay, selections etc. in vector data Spatial Data nalysis Input -> spatial operation -> Output Sequences for complex analyses Spatial Data nalysis One-to-one; Many-to-many 2

3 Scope of Vector Operations Vector Operations Measurement Selection, Classification, & Dissolve uffer Overlay Point in polygon Line in polygon Polygon Intersection Union Clip Identity Measurement Length (Lines) by Pythagorean theorem D 2 x x y y1 1 D 2 rea (Polygons) C by dividing the polygon into triangles whose areas can easily be calculated 0,0 D CD = C0 + CD0 0 D0 3

4 Vector Operations Measurement Selection, Classification, & Dissolve uffer Overlay Point in polygon Line in polygon Polygon Intersection Union Clip Identity Selection (Query) (1) Select features based on attributes only (2) Select features based on spatial criteria such as djacency, overlap or containment: No new geometry created (tbd in overlay ) Within example counties in CO; corn for select by location What means djacency 4

5 Selection (Query) Can also set selection conditions using: Set algebra: <, >, =, <> oolean algebra: disjunction (OR) conjunction (ND) complement/negation (NOT) Let s see one example how this works: Sel capitals in C and CO counties selected & export selected F Example for spatial containment Sel C counties and road within (Re-)Classification Categorize geographic objects based on a set of conditions (reclassification, recoding). e.g. nderson Land Cover classification (nderson et al., 1976): 1 urban or built-up 2 agricultural 3 rangeland 4 forest deciduous forest 42 evergreen forest 43 mixed forest Show NLCD 5

6 Re-Classification (binary) Problem of precision of belonging to one class or the other Ex. Dissolve selected C counties and by attribute Classification Schemes Quantiles Show on US counties, pop

7 Modifiable real Unit Problem (MUP) ggregate values from groups of polygons depend on size (size effect) and shape (zoning effect) of the aggregated polygons. Example: Openshaw & Taylor (1979): Percentage of elderly voters and the number of Republican voters in all counties of Iowa Correlations between 0.98 and with varying aggregation levels of counties Dissolve counties to states with sum pop 2010, and compare pop class. For state and county nalytical Scale Census tracts Counties Number of households in Indiana (spatial distribution) Census data and anonymity (data confidentiality) Intra-zonal variation Sensitivity tests to estimate the impact of MUP 7

8 Dissolve Combine like features based on attributes. 2 3 Polygon Dissolve grain crops 2 orchards 3 residential 4 commercial voiding unneeded and redundant information 1 agricultural 2 non-agricultural Dissolve often used after reclassification oundaries are removed when they separate states with the same value. The dissolve attribute is_west. Vector Operations Measurement Selection, Classification, & Dissolve uffer Overlay Point in polygon Line in polygon Polygon Intersection Union Clip Identity 8

9 uffer Spatial definition of what is within a given proximity Dissolve, overlap and nesting Doughnut uffer e.g. within 10 meters but not within 5 meters E.g., from nested buffers uffer polygon 5 10 Hole 9

10 Example buffer around selected roads with and w/out dissolve opt. Multiple ring buff outside option for polys Vector Operations Measurement Selection, Classification, & Dissolve uffer Overlay Point in polygon Line in polygon Polygon Intersection Union Clip Identity Final ex: buff cap in C and CO, buffer 5 degrees and select all counties within or intersect with this buffer Spatial nalysis: Overlay Combination of different data layers oth spatial and attribute data are combined Requires that data layers use a common coordinate system new data layer is created 10

11 Overlay rguably the most important GIS analysis function Vector Overlay Three types of overlay: Point in polygon Line in polygon Polygon (polygon on polygon) Output typically takes the lowest dimension of the inputs For example: Point in Polygon results in a point Overlay: Point in Polygon Trees Land Cover NewTrees C = C Point Table ID Tree Elm Maple C Elm Poly Table ID Cover 1 Rural 2 Urban Point Table ID Tree Cover Elm Rural Maple Rural C Elm Urban 11

12 Overlay: Point in Polygon Overlay: Line in Polygon Streets Land Cover NewStreets C + = 1 2 D C Line Table ID Street Race Race C rch Poly Table ID Cover 1 Rural 2 Urban Line Table ID Street Cover Race Rural Race Urban C rch Urban D Race Urban Overlay: Polygon on Polygon Intersection (ND) Union (OR) Identity Only overlapping features included in output ll data included in output Clip identity layer to input layer & add identity attributes to input 12

13 Polygon Overlay: Intersection griculture Land Cover <Intermediate> ID Owner rown Smith ID Cover commercial industrial rea of intersection New node Polygon Overlay: Intersection <Intermediate> Output rea of intersection New node ID Owner Cover rown commercial Smith industrial Polygon Overlay: Union griculture Land Cover <Intermediate> ID Owner rown Smith ID Cover commercial industrial rea of union New node 13

14 Polygon Overlay: Union <Intermediate> Output C D E rea of union New node Desktop help! ID Owner Cover commercial rown commercial C rown D Smith E Smith industrial Polygon Overlay: Clip Clip feature must be polygon, input can be points, lines, or polygons Input attributes retained; clip feature attributes ignored Polygon Overlay: Erase Erase and input features of same type Input attributes retained; erase feature attributes ignored 14

15 griculture (input layer) Polygon Overlay: Identity Land Cover (identity layer) <Intermediate> ID Owner rown Smith ID Cover commercial industrial rea of identity New node Clips identity layer to input layer & adds identity attributes Defining IDENTITY : Rules of proportions/majority of areas etc Polygon Overlay: Identity <Intermediate> Output C D rea of identity New node ID Owner Cover rown commercial rown C Smith D Smith industrial Polygon Overlay Problem Common features in vector overlays often create Slivers or Sliver polygons - polygons don t line up due to subtle differences (e.g. different time, source, materials) - only visible when zoomed in - consume little space but affect analytical results. 15

16 Summary Measurement Selection, Classification, & Dissolve uffer Overlay What is the form/dimension of the output? Point in polygon Line in polygon Polygon Intersection Union Clip Identity 16