San Luis Obispo County Planning and Building Department Jeff Legato Mapping and Graphics Specialist

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?  County planning is updating the Land Use and Circulation Element of the General Plan  Need understanding of:  Potential housing units  Potential population  Water usage  Necessary land use acreage  Necessary park facilities  Police and fire requirements  Necessary school facilities  etc etc

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 all depends… Rube Goldberg is the ® and © of Rube Goldberg, Inc.

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 areas between two datasets and outputs a table.  14 planning areas  Tip – Can’t add columns together if one of them has a 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 create points from lines and polygons…  Intersect roads with URL 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" 25')) OR ( "URL_RDMI" = ' ' AND ( "VRL_RDMI" = '5 - 10' OR "VRL_RDMI" = ' ' OR "VRL_RDMI" = ' ' OR "VRL_RDMI" = ' ' 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

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