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Maps as Site Analysis Tools

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Overlays ecosystem components in order to estimate development suitability. Highlights both: ... drew composite suitability map. GIS-'computing' ... – PowerPoint PPT presentation

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Title: Maps as Site Analysis Tools


1
Maps as Site Analysis Tools
  • Overlaying Slope, Drainage, Soils, Vegetation
    Maps to Identify Development Opportunities
    Constraints

2
Todays Agenda
  • Reading maps
  • Location
  • Topographic
  • Soils
  • Vegetation
  • Synthesizing map info
  • Slope
  • Drainage
  • Making suitability maps
  • Graphic overlay analysis (Ian McHarg)
  • Computer overlay models (ArcView Spatial Analyst)

3
Locational Structure
4
The U.S. Grid
5
USGS 7.5 Minute Quads Contours, Features
Scale 124,000 (about .4 mile to the inch)
Contour interval 10 feet
6
Reading a Topo Map
7
Interpreting Contours
8
Interpreting Contours
9
Determining water flow direction
Which way does water flow? Hint always
downhill!!
10
Why Investigate Soils?
11
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12
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13
Horizons
  • 0 Horizon - Organic
  • A Horizon - Mineral Horizon mixed with organics
  • B Horizon - Mineral Horizon changing layer
  • C Horizon - Mineral Layer
  • R Horizon - Consolidated rock

14
Cross Section of Soils Horizon
15
Cross Section with Soil Types
16
Erosion Forms New Horizons
17
Soils Surveys
  • Report defines
  • Types of soils
  • maps of soils
  • Suggested use and management

18
U.S. Natural Resources Conservation Service (old
SCS)
Scale usually 1 20,000
Soil type slope
19
Soil Properties of Concern
  • Bearing capacity
  • Shrink swell
  • frost penetration
  • slope failure

20
Bearing Capacities
  • Bed Rock 200 kips/sq ft
  • Sedimentary Rock 30
  • Compacted gravel 20
  • Loose gravel 8
  • Stiff clay 8
  • Soft clay 2
  • (1 kip 1000 pounds)

21
Angles of Repose
22
Soil Engineering Ratings
  • Building sites (stability, bearing capacity)
  • Sanitary facilities (septic systems)
  • Construction materials (sand, gravel)

  • Drainage (wetlands, floodplains)
  • Recreational areas
  • Compaction characteristics
  • Erosion potential
  • pH

23
Shear, Compression, Workability, Permeability
24
Vegetation Tree Types
Darker mature woods specimen trees
25
Synthesizing Slope from Topo
  • Slope maps are derived by converting distance
    between contour lines into percent (planning use)
    or degree (engineering use) classes or intervals
  • Unconstrained (0-14)
  • Moderate (15-25)
  • Steep (26 or greater)
  • Closer the contour lines, steeper the slope!

26
Visualizing Slope
25 slope rises 25 feet in 100 feet horizontally
27
Deriving Slope
  • Slope vertical rise in feet for every 100 feet
    of horizontal distance
  • Slope Run/Rise x Contour interval
  • Classes
  • Unconstrained 0-15 100/15 x 1 6.7 between
    1 contours (13.4 for 2 contours)
  • Moderate 15-25 100/25 x 1 4-6.7
  • Steep 26 up 100/26 x 1 3.9 or less

28
Making a Slope Map by Hand
29
Deriving Drainage from Topo
  • Water runs downhill (until Law of Gravity
    repealed) follows shortest path (perpendicular
    to contour lines)
  • Water runs off ridges collects in swales,
    streams, ponds, floodplains
  • Watersheds basins bounded by ridge lines
  • Contours in swales point upstream, indicate
    direction of water flow

30
Making a Drainage Map
Ridge line
31
Site Suitability Analysis
  • Purpose
  • Identify map separate ecosystem components
    (soil, vegetation, hydrology, etc.)
  • Understand relationships among components (e.g.,
    how slope soil interact to affect erosion,
    building sites, etc.)
  • Determine suitability of site areas for various
    land uses, based on component combinations
  • Not a design plan but an indication of
    opportunities and constraints
  • History
  • Developed in 1960s by landscape architect, Ian
    McHarg (author of Design With Nature)

32
Suitability Analysis Approach
  • Overlays ecosystem components in order to
    estimate development suitability
  • Highlights both
  • Site amenties (nice views, water, trees,
    orientation, buildable areas, good access)
  • Site constraints (bad views, steep slopes, wet
    areas, unstable soils, noise, poor access)

33
Site Suitability Map
34
From Design With Nature to GIS
  • McHarg-eyeballing
  • overlaid sheets of tracing paper (1 for slope,
    soils, etc.),
  • determined suitability by visual inspection
    (e.g., darkest areas),
  • drew composite suitability map
  • GIS-computing
  • uses computer to overlay registered layers of
    digital data,
  • can add weights if desired,
  • determines suitability mathematically,
  • makes composite map

35
Suitability Model Opportunities
  • Slope moderate, unconstrained (0-15)
  • Drainage not in drainage courses, floodplains
  • Soils stable, well drained
  • Vegetation hardwoods
  • Model additive, weighted/ unweighted
  • Suitability
  • High (flat, accessible, dry, stable, views, etc.)
  • Moderate (medium slope, accessible, mostly
    dry/stable, etc.)
  • Low (steep, wet, poor soil, difficult access)
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