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Spatial Data Analysis: Districting, Regionalization, and Proximity Calculations, Study notes of Geology

Aligarh Muslim UniversityGeology

An overview of various spatial data analysis techniques, including districting, regionalization, and proximity calculations. Districting involves grouping contiguous or non-contiguous polygons into districts, preserving or dissolving original boundaries. Regionalization groups polygons into contiguous regions, dissolving original boundaries. Proximity calculations determine distances between points and features. Tools like arcview 8 and commands such as pointdistance, near, spatial joins, and overlays are used for these analyses.

Typology: Study notes

2012/2013

Uploaded on 07/23/2013

ramkumar
ramkumar 🇮🇳

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Criteria may be:
–formal (based on in situ characteristics)
e.g. city neighborhoods
–functional (based on flows or links):
e.g. commuting zones
Groupings may be:
–contiguous
–non-contiguous
Boundaries for original polygons:
–may be preserved
–may be removed (called dissolving)
Examples:
•elementary school zones to high school
attendance zones (functional districting)
•election precincts (or city blocks) into
legislative districts (formal districting)
•creating police precincts (funct. reg.)
•creating city neighborhood map (form. reg.)
•grouping census tracts into market
segments--yuppies, nerds, etc (class.)
•creating soils or zoning map (class)
Implement in ArcView 8 thru
Tools/Geoprocessing Wizard, using
dissolve features based on an attribute
Spatial Operations:
spatial aggregation
•districting/redistricting
–grouping contiguous polygons
into districts
–original polygons preserved
•Regionalization (or dissolving)
– grouping polygons into
contiguous regions
– original polygon boundaries
dissolved
•classification
–grouping polygons into non-
contiguous regions
–original boundaries usually
dissolved
–usually ‘formal’ groupings
Grouping/combining polygons—is
applied to one polygon layer only.
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Criteria may be:

  • formal (based on in situ characteristics) e.g. city neighborhoods
  • functional (based on flows or links): e.g. commuting zones Groupings may be:
  • contiguous
  • non-contiguous Boundaries for original polygons:
  • may be preserved
  • may be removed (called dissolving) Examples:
  • elementary school zones to high school attendance zones ( functional districting )
  • election precincts (or city blocks) into legislative districts ( formal districting )
  • creating police precincts ( funct. reg .)
  • creating city neighborhood map ( form. reg. )
  • grouping census tracts into market segments--yuppies, nerds, etc ( class. )
  • creating soils or zoning map ( class ) Implement in ArcView 8 thru Tools/Geoprocessing Wizard, using dissolve features based on an attribute

Spatial Operations:

spatial aggregation

  • districting/redistricting
    • grouping contiguous polygons into districts
    • original polygons preserved
  • Regionalization (or dissolving)
    • grouping polygons into contiguous regions
    • original polygon boundaries dissolved
  • classification
    • grouping polygons into non- contiguous regions
    • original boundaries usually dissolved
    • usually ‘formal’ groupings Grouping/combining polygons—is applied to one polygon layer only.

Districting : elementary school attendance zones grouped to form

junior high zones.

Regionalization : census tracts grouped into neighborhoods

Classification : cities categorized as central city or suburbs

soils classified as igneous, sedimentary, metamorphic

Proximity Calculations, page 2

• NEAR computes the distance from each point

in a coverage to the nearest arc, point or node

in another coverage.

NEAR <in_cover> <near_cover> {LINE |

POINT | NODE} {search_radius} {out_cover}

{NOLOCATION | LOCATION}

Arc: near well stream line 1500 wellstr

location

The PAT of the output coverage will have two additional items: one to store the distance to the nearest feature in the near_cover, and a second to store the internal number of the nearest feature. LOCATION adds items for x and y coordinates.

Spatial Operations: Spatial Matching: Spatial Joins and Overlays

  • combine two (or more) layers to:
    • select features in one layer, &/or
    • create a new layer
  • used to integrate data having different spatial properties (point v. polygon), or different boundaries (e.g. zip codes and census tracts)
  • can overlay polygons on:
    • points ( point in polygon)
    • lines ( line on polygon )
    • other polygons (polygon on polygon)
    • many different Boolean logic combinations possible » Union (A or B) » Intersection (A and B) » A and not B ; not (A and B)
  • can overlay points on:
    • Points, which finds & calculates distance to nearest point in other theme
    • Lines, which calculates distance to nearest line Examples - assign environmental samples (points) to census tracts to estimate exposure per capita (point in polygon) - identify tracts traversed by freeway for study of neighborhood blight (polygon on lines) - integrate census data by block with sales data by zip code (polygon on polygon) - Clip US roads coverage to just cover Texas (polygon on line) - Join capital city theme to all city theme to calculate distance to nearest state capital (point on point)

CLIP

  • CLIP - extracts those features from an input coverage that

overlap with a clip coverage. This is the most frequently

used polygon overlay command to extract a portion of a

coverage to create a new coverage.

CLIP <in_cover> <clip_cover> <out_cover> {POLY | LINE | POINT | NET | LINK | RAW} {fuzzy_tolerance} The <clip_cover> must have polygon topology. Boundaries of interior polygons in the <clip_cover> are not used in CLIP. CLIP uses the clip coverage as a cookie cutter ; only those input coverage features that are within the clip coverage are stored in the output coverage. Topology is built for the output coverage. Only the attributes of the in_cover are retained in the out_cover

CLIP, pg 2

ERASE

  • ERASE - erases the input coverage features that

overlap with the erase coverage polygons.

ERASE <in_cover> <erase_cover> <out_cover> {POLY | LINE | POINT | NET | LINK | RAW} {fuzzy_tolerance} The <erase_cover> must have polygon topology. Boundaries of interior polygons in the <erase_cover> are not used in ERASE. The polygons of the erase coverage define the erasing region. Input coverage features that are within the erasing region are removed. The output coverage contains only those input coverage features that are outside the erasing region. Erase is the opposite of clip: it leaves you with “the left over dough” Topology is rebuilt for the output coverage.