san luis obispo county planning and building department jeff legato mapping and graphics specialist...
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San Luis Obispo County
Planning and Building Department
Jeff Legato
Mapping and Graphics Specialist
805-781-5102
GIS Rural Subdivision Potential What? -- Rural subdivision potential Why? -- General Plan Update How? -- ESRI Model Builder
GIS Rural Subdivision Potential What is Rural Subdivision Potential?
Why subdivision potential?
Build-out The possible amount of development
allowed by the General Plan
Traditional build-out analysis Add up all land use by type and divide by
allowed density. Subtract out differing percentages for roads, vacancy
rates etc.
Not very realistic Relies on multiple gross general assumptions Doesn’t take into account existing lot sizes Can’t take into account multiple densities
Build-Out
Multiple densities? Rural Land (RL)
20 40 80 160 320
It alldepends…
Rube Goldberg is the ® and © of Rube Goldberg, Inc.www.RubeGoldberg.com
Build-Out
Requires generation of data for inputs Separate models created for…
Soil class acreage for each AG parcel by type Road miles to URL and VRL boundaries Fire hazard zones and response times Geologic Study Areas Average slope for each rural parcel
GIS to the Rescue!
ESRI model builder Spatial Analyst Network Analyst
ESRI Model Builder Located in ArcCatelog
Click to build new model
Click to bring up ArcToolbox
ESRI Model Builder Drag and drop processes and
feature classes Connect the dots and run
Click to connect processes
Recall Subdivision inputs
Soil acreage by class for each AG parcel Average Slope for each parcel Remoteness in road-miles to URL and VRL Fire Hazard, Fire Response Time, and GSA
Tools used Soil data
Tabulate Area (Spatial Analyst Required)
Calculates cross-tabulated areasbetween twodatasets and outputsa table.
14 planning areas Tip – Can’t add
columns togetherif one of them hasa null value
Tools used Average Slope
Zonal Statistics (SA Extension Req.)
Summarizes values of a raster (slope DTM) by zone (parcels)
Tools used Road Miles
Network Analyst Extension Service Area polygons Needs points to route to
How to createpoints from linesand polygons…
Intersect roads withURL boundaries
Tools used Fire response/hazard and Geologic Study Area
Select and calculate based on location
Tools used Select by attributes Simple matter of selecting parcels that meet the
criteria and tagging them with the allowed density… ("avg_slope" > 30 AND ("GSA_FZ" IS NULL AND
"GSA_LQLS" IS NULL)) OR ("avg_slope" <= 30 AND ("GSA_FZ" = 'GSA Seismic Hazard Area' OR "GSA_LQLS" = 'GSA Geologic Hazard Area')) OR ((( "VRL_RDMI" = '5 - 10' AND ( "URL_RDMI" = '20 - 25' OR "URL_RDMI" = '> 25')) OR ( "URL_RDMI" = '15 - 20' AND ( "VRL_RDMI" = '5 - 10' OR "VRL_RDMI" = '10 - 15' OR "VRL_RDMI" = '15 - 20' OR "VRL_RDMI" = '20 - 25' OR "VRL_RDMI" = '> 25' ))))
Tip Subdivisions are whole numbers and are rounded
down. 1 * INT ([ACRES] / 20) INT – Removes all decimal places leaving a whole
number and rounds down.
San Luis Obispo County
Planning and Building Department
Jeff Legato
Mapping and Graphics Specialist
805-781-5102
GIS Constraints Analysis
Groundwater Agricultural Public Safety
Protected Resources Other Compilation