Arizona State University Using GIS to Generate Mutually Exclusive Service Areas Linking Travel On and Off a Network Christopher Upchurch Michael Kuby Michaek Zoldak Anthony Barranda Arizona State University

Light Rail Research Station Area Factors Service Area Requirements Walking Distance Mutually Exclusive Network Based

Available Buffering Techniques Euclidian Buffers Circular

Circular Buffers

Available Buffering Techniques Euclidian Buffers Circular Thiessen Polygon

Thiessen Polygon Buffers

Available Buffering Techniques Euclidian Buffers Circular Thiessen Polygon Combined Circular and Thiessen Polygon

Combined Circular and Thiessen Polygon Buffers

Available Buffering Techniques Euclidian Buffers Circular Thiessen Polygon Combined Circular and Thiessen Polygon Network Based Buffers ArcView Network Analyst

ArcView Network Analyst Service Areas

ArcView Network Analyst Service Areas

ArcView Network Analyst Service Areas

Available Buffering Techniques Euclidian Buffers Circular Thiessen Polygon Combined Circular and Thiessen Polygon Network Based Buffers ArcView Network Analyst ArcView Network Analyst + Thiessen Polygon

Service Area Requirements Walking Distance Mutually Exclusive Network Based

LOON Method Linked On-Off Network Method Raster Based Hierarchical Approach Distance Off the Network Distance On the Network

Step 1: Initialization Network Impedance Grid Source Grid Off-Network Impedance Grid

Network Impedance Grid

Source Grid

Off-Network Impedance Grid

Step 2: Calculate Lowest Network Distance Cost Distance Command Finds: Closest Source Node for Each Cell Distance to that Source Node Using: Source Grid Network Impedance Grid Output: Raw Distance Grid Allocation to Source Node Grid

Raw Distance Grid

Allocation to Source Node Grid

Step 3: Create a New Set of Source Cells Hierarchical Approach Distance On the Network Distance Off the Network New Source Cells for Second Cost Distance Command

Raw Distance Grid

All-Network Source Grid

Step 4: Calculate Off-Network Distance Cost Distance Command Using: All-Network Source Grid Off-Network Impedance Grid Output: Off-Network Distance Grid On-Network Distance Grid

Off-Network Distance Grid

On-Network Distance Grid

Step 5: Calculate Total Distance Off-Network Distance + On-Network Distance

Total Distance Grid

Step 6: Trim and Reclassify the Total Distance Grid Reclassify all cells less than maximum distance as 1 Reclassify all cells more than maximum distance as “no data”

Buffer Mask Grid

Step 7: Create Final Buffers Buffer Grid = Allocation to Source Node Grid x Buffer Mask Grid

Buffer Grid

Proof of Concept What Benefits does the LOON method have over other techniques for generating service areas?

LOON Service Areas

LOON vs. Circular + Thiessen

LOON vs. ArcView + Thiessen

Statistical Comparisons ArcView vs. LOON Employment of Sacramento buffers calculated using both methods Citywide average area and employment fairly close, within 5% Average percentage difference greater than 85%

Questions? Step by Step Instructions are available at: http://geography.asu.edu/mkuby/gis_buffer_steps.html Questions?