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Vector Analysis

Vector Analysis. Ming-Chun Lee. Spatial Analysis. What is Spatial Analysis? Spatial analysis is a set of methods whose results change when the locations of the objects being analyzed change. Turning raw data into useful information Reveal things that might otherwise be invisible.

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Vector Analysis

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  1. Vector Analysis Ming-Chun Lee

  2. Spatial Analysis • What is Spatial Analysis? • Spatial analysis is a set of methods whose results change when the locations of the objects being analyzed change. • Turning raw data into useful information • Reveal things that might otherwise be invisible

  3. Spatial Analysis • Turning raw data into useful information • Extracting or creating new information about a set of geographic features and examining the relationships between them. • The set of geographic features used in spatial analysis could pertain to data within only one layer or within two or more layers depending upon the users needs.

  4. Spatial Analysis • Methods range from simple to sophisticated • Usually involves manipulations or calculation of coordinates or attribute variables with a various operators (tools), such as: • Selection • Measuring • Reclassification • Dissolving • Overlay • Buffering

  5. Selection • Can be invoked on spatial and attribute components • Selection by Attributes • Selection by Locations • Involves selective search • No new objects created • example: lots owned by foreigners (attribute) • example: lots along the substation buffer (location)

  6. Measurements • Getting numerical values that describe aspect of data • Length • Area • Many tasks require measurement from maps • measurement of distance between two points • measurement of area, e.g. the area of a parcel of land

  7. Reclassification • Classification - identify a set of characteristics to group together objects. • In a vector system, classification involves addition of objects characteristics. (join a table) • In a raster system, classification involves converting or coding cell values. • Classification examples: Land parcels for housing are classed into single-family and multi-family • Classification provides new patterns/relationships

  8. URBAN RESIDENTIAL URBAN INDUSTRIAL URBAN RURAL AGRICULTURE RURAL RURAL FOREST GENERALIZED CLASSIFICATION ORIGINAL CLASSIFICATION Reclassification

  9. Overlay Analysis • Combination of different data layers • Both spatial and attribute data is combined • Produces new layers • Involves two or more data layers • You can only overlay or analyze two themes • But you can combine two into one and then deal with the third one and so one; input theme can be point/line/polygon, but overlay needs to be a polygon • All themes need to be spatially registered • Need to have same coordinate system

  10. Overlay Analysis • Until the arrival of GIS • Map overlay analysis was performed manually • Superimposing transparent map layers on a light table to identify sites simultaneously meeting a number of criteria • Overlay operations can be performed in vector/ raster-based GIS • Overlay operation is a key analytical capability of a GIS • New data can be created by combining two or more input data

  11. Overlay Analysis

  12. Overlay Analysis

  13. Vector vs. Raster • Vector Overlay • Raster Overlay URBDP 498w - Introduction to GIS in Planning

  14. Vector Overlay • Based on geometry and topology • Vector overlay operation results in a more complex output layer • More polygons / intersections / line segments than input layers • Calculates new topology and associated attributes • More time-consuming, complex and computationally expensive, in comparison with raster-based overlay operations

  15. Raster Overlay • Cell by cell process which results in the combination of the two input layers • known as map algebra • operations include boolean, multiply, and algebra

  16. Three Types of Vector Overlay • Point-in-Polygon • Points are assigned attribute of polygon • E.g. wildlife (point) and assoc. with vegetation (poly) • Line-in-polygon • Original lines are dissected by polygon boundary • Lines will have attribute of lines and polygons • E.g. roads and soil types along roads • Polygon-on-polygon • Each new polygon will have attribute from both • E.g. elevation and vegetation or elevation and rainfall

  17. Boolean Logic • Determines the binary properties of features • True-false, yes-no, or presence-absence • Rather than using numbers and magnitudes of features • Reduces measures to some binary condition • Simplifies the results of overlay operations

  18. Boolean Logic A NOT B A A&B B B NOT A • Union (A or B) • Intersection (A & B)

  19. Boolean Logic

  20. Buffering • Common GIS operation • A type of proximity analysis where a buffer zone is created to perform a search • Buffer: encloses point, line, or polygon at specified distance. • Search: specify a distance from a point (radius), line (corridor), area (area) • New spatial objects created

  21. Buffer Generation • Buffering a Point • All area within one mile of a city • Buffering a Line • All areas within 100 meters of a road • Buffering an Area • All areas within 500 meters of a wetlands area.

  22. Buffer Generation • Buffering possible with raster or vector data models

  23. Vector Analysis • Overlays for Trimming Diverse Layer Extents • CLIP • ERASE • Combining Similar Layers with Different Extents • MERGE • UPDATE • Creating Proximity-Based Polygon Layers: BUFFER • Dissolve • ArcMap Dissolve Regions • ArcToolbox Dissolve • Overlays for Merging Diverse Layers • UNION • INTERSECT • IDENTITY

  24. DISSOLVE (I) • ArcMap • GeoProcessing Wizard • Operates onShapefiles, Coverages • Merges Non-Adjacent Polygons A D C B E D A C D

  25. DISSOLVE (II) • ArcToolbox • Dissolve • Operates on Coverages • Doesn’t Merge Non-Adjacent Polygons A D C B E D A C E

  26. UNION • Combine Only the CommonExtents of Both Layers • Preserve All Attributes URBDP 498w - Introduction to GIS in Planning

  27. INTERSECT • Combine Full Extents of Both Layers • Preserve All Attributes

  28. IDENTITY • Combine Only the Extents of the Original Layer • Preserve All Attributes URBDP 498w - Introduction to GIS in Planning

  29. CLIP • Trim the Original Layer to Only the Extents of the Clip Layer • Preserve Only the Original Layer’s Attributes URBDP 498w - Introduction to GIS in Planning

  30. ERASE • Trim the Original Layer to Exclude the Extents of the Clip Layer • Preserve Only the Original Layer’s Attributes URBDP 498w - Introduction to GIS in Planning

  31. MERGE/APPEND • Add Non-Overlapping Extents of Multiple Layers • Preserve Consistent Attributes

  32. UPDATE • Add Overlapping Extents of Multiple Layers • Preserve Consistent Attributes • Within Shared Extents, Give Preference to Newer Layer

  33. Summary of Overlay Operations

  34. BUFFER • Create a Polygon Layer with Boundaries at a Specified Distance from Another Layer • Fixed Distance • Variable Distance Based on an Attribute • Series of Buffers

  35. BUFFER • Fixed Distance • Examples: • Walking Distance to Bus Stops • Areas of Street Light Illumination

  36. BUFFER • Variable Distance Based on an Attribute • Examples: • Noise Levels By Street Type

  37. BUFFER • Series of Buffers • Examples: • Walking Distance to Bus Stops • Areas of Street Light Illumination

  38. Tools for Spatial Analysis • All of these tools are found in ArcToolbox in ArcMap

  39. Example of Vector-Based Analysis • Find suitable sites for a new arboretum • Site Criteria: • Within county limit • Deep, Fertile, Loamy Soils • Forested Land • More than 1 km from major rivers • Between 2 and 4 kms from major roads

  40. County Boundary

  41. Major Roads Clipped to County

  42. Major Rivers Clipped to County

  43. Buffer Rings on Roads 2-4 km

  44. Buffer of Roads >2km <4km

  45. Land Use

  46. Forest Land Cover

  47. Clip Forest LC to Roads

  48. County Soils

  49. Deep, Fertile, Loamy Soils

  50. Clip Soils to Roads

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