Border around project area
Everything else is hardly
noticeable… but it’s there
Big circles… and semi-
transparent
Color distinction is
clear
Spatial Analysis
» Spatial analysis refers to the formal techniques to conduct analysis using their topological, geometric, or geographic properties.
» In a narrower sense, spatial analysis is the process of analyzing geographic data.
» Types of spatial analysis you have already been doing:˃ Buffering˃ Select by location
» Layers can be overlaid - placed one over the other based on a shared geographic reference – allows analysis of the relationships between layers
Raster Data
» Why do we have to use raster data?˃ Vector data (points, lines and polygons) are limited to only certain
spatial analyses+ Point in polygon (which points are within+ Line intersections
˃ Vector data only knows about the space it occupies
» Raster data covers the entire region» Provides a more powerful format for advanced
spatial and statistical analysis
Raster Data
» A matrix of cells» Rows and columns
(grid)» Examples: aerial
photographs, digital photos, scanned maps
» Examples in spatial analyst…
The grid data structure
» Grid size is defined by extent, spacing and no data value information˃ Number of rows, number of column˃ Cell sizes (X and Y) ˃ Top, left , bottom and right coordinates
» Grid values ˃ Real (floating decimal point)˃ Integer (may have associated attribute table)
So now that I know what a raster is… what can I do with it?
» derive new information from your existing data, » analyze spatial relationships, » build spatial models, and » perform complex raster operations.
Applications of spatial analysis
» Find suitable locations» Model and visualize crime
patterns » Analyze transportation corridors» Perform land use analysis » Conduct risk assessments» Predict fire risk» Determine erosion potential » Determine pollution levels» Perform crop yield analysis
How to find “suitable” locations
» Step 1: State the Problem˃ Find the most suitable location for a new long-term care facility in Long
Beach
» Step 2: Identify the Parameters and Weight˃ Supply: needs to be far from existing facilities (weighted by number of
beds in the facilities) (25%)˃ Demand: number of persons over 65 (50%)˃ Access: close to major streets (25%)
» Step 3: Prepare Your Input Datasets˃ Long Beach Facilities (point)˃ Census Tracts – Age>65 (polygon)˃ Major Streets (line)
» Step 4: Perform the Analysis
ArcGIS Workflow
» ArcCatalog: ˃ Make sure all your layers are in the same projection (eg: UTM Zone 11N)
» ArcMap: 1. Load all your layers, double check that you are on the right projection
and units (eg: miles)2. Turn on Spatial Analyst Toolbar3. Set the Environment (very important, ensures that raster layers have the
same cell size!)4. Load your indicator layers5. “Rasterize” your layers (Ex: Kernel Density, Feature to Raster, Euclidean
Distance)6. Reclassify7. Apply weights8. Generate final raster
Step 2Check the map units*Even if you change the “display” units, spatial analysis will be conducted using the “map” units
Step 4Set the environment1. Processing Extent
Usually set this to the extent of your project, or the largest layer
2. Raster AnalysisCell size and Mask
Best site for new facility
Kernel Density on Number of
Beds
Feature to Raster on Age>65
Euclidean Distance
Long Beach Facilities
Long Beach Census Tracts
Long Beach Major Roads
Far from existing facilities
Close to areas with high
numbers of senior citizens
Close to major streets
25% 50% 25%
Long Beach Facilities
Long Beach Census Tracts
Long Beach Major Roads
Kernel Density on Number of
Beds
Feature to Raster on Age>65
Euclidean Distance
Reclassify:3 most desirable
1 = least desirable
Reclassify:3 most desirable
1 = least desirable
Reclassify:3 most desirable
1 = least desirable
3 3
1 3
3
2
1 1 2
1 1
1 2
3
3
2 2 3
2 1
2 1
3
1
2 2 1
3 3
1 3
3
2
1 1 2
1 1
1 2
3
3
2 2 3
2 1
2 1
3
1
2 2 1
Long Beach Facilities
Long Beach Census Tracts
Long Beach Major Roads
25%
50%
25%
.75 .75
.25 .75
.75
.5
.25 .25 .5
.5 .5
.5 1
1.5
1.5
1 1 1.5
.5 .25
.5 .25
.75
.25
.5 .5 .25
1.75 1.5
1.25 2
3
2.25
1.75 1.75 2.25
Spatial Analysis Tools > Map Algebra > Raster Calculator
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