Williamson Map Rectification

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Mapping/GIS Projects with Documented Return on InvestmentAppraisal Map Evolution

Williamson County StatisticsMaps & Records Department StatisticsMaps & Records Department TimelineGIS Project Benefits

Williamson Central Appraisal DistrictGeorgetown, Texas

Where are we?

Williamson County Statistics

Williamson County Statistics

Growth Rate State of Texas

Williamson County Population F 1970 - 2010 Williamson County Statistics

Growth Rate Austin Metro Area 2000 2010 37%Williamson County Rate2000 201069 %1990 2010203 %1980 2010452%1970 20101,033%

Williamson County Statistics

Growth Rate 9th fastest growing county in the nation in 2009.Williamson County Statistics

Growth Rate New Sub Lots 10 Year Average = 7,100 per yearWilliamson County Statistics

Williamson County Statistics

Growth Rate New Improvements10 Year Average = 5,835 per year

1993 Mylar Map Maintenance

Maps & Records Department Timeline

1993 WCAD has desire to begin GIS project1994 GIS Pilot Project completedPurchased used PCs, free software from vendorNo GIS budget1995 All map maintenance digital - no more drafting!Traded a set of paper maps for scanned images100% digital raster/vector hybrid mappingConversion progress limited to map updates onlyNo GIS budget1996 Parcel conversion process very s-l-o-wNo GIS budget Chief Appraiser retires

Maps & Records Department Timeline

1997 Begin Phase I Parcel Conversion ProjectLimited GIS budgetNew Chief Appraiser hired1998 Phase I Parcel Conversion Project CompleteRealistic GIS budget (conversion funding)100% vector mapsBegin GIS software analysis training FAILURE.1999 Begin Phase I Network Infrastructure UpgradeBegin replacing ALL dumb terminals with PCsGIS budget includes analysis software & trainingNo aerial imagery budget

Maps & Records Department Timeline


2000 Complete Phase I Network Infrastructure UpgradeWCAD hires vendor to host www.wcad.orgWebsite with interactive mapping Tried In-house geo-referencing FAILURE Record number of new subs filed (over 9,000)2007 Begin Phase II GIS Conversion Project (software)GIS budget (software conversion funding)Joined consortium to purchase oblique imagery 2008 - Complete Phase II GIS Conversion Project (software)Received first set of oblique imageryGIS budget includes software & training dollarsRe-train M&R GIS staff on new softwareBegin parcel maintenance using new GIS software

Maps & Records Department Timeline


2009 Begin/Complete Phase III GIS Conversion Project (rectification)Oblique & ortho imagery in budget (6 years)Parcel rectification complete!Change detection funding in budgetSketch verification initialized (all improved property)2010 Utilize GIS toolsAppraisal analysis/defenseChange detection utilizedSketch validation for new improvements only

Maps & Records Department Timeline


Parcel layer not user friendly to our staff or taxing units prior to 2008.Our parcel layer required several tools to take from deed to map and additional tools to analyze data.The maps created were in an uncommon format not useable to our taxing unitsConversion to GIS system that Taxing Units were using became necessary.Streamlined internal processCreated useable maps for our taxing unitsConversion to Common GIS Mapping Software to Benefit Efficiency & Taxing Units



Our data was then in a common format with the Taxing Units but required additional manipulation to be useful.Taxing Units still had to rectify our parcel layer.Unprofessional appearance to the public and other users implied that our map work was less than trustworthy.Answer = Parcel RectificationStudies conducted to determine feasibility of doing this rectification internally proved to be cost prohibitive.Early 2009 we published a Parcel Rectification RFP.Late 2009 rectified parcel layer completed.Enabled Taxing Units to use our parcel layer without additional work and created professional and accurate appearance to maps which in turn increased our credibility.

Common Mapping Software but.... Parcel Layer Not Geo-referenced


Parcel Rectification Before & After


Consortium formed between larger taxing units and appraisal district to purchase imagery.Pros: Cost sharingCons: Imagery only available to those who participatedLack of complete control for appraisal districtAppraisal District purchase of imageryPros: Shared cost through contributions via appraisal district budgetComplete control of imagery by appraisal districtImagery available to ALL taxing unitsCons:Cost prohibitive to appraisal district if taxing units do not see the benefit

Ortho & Oblique Aerial Imagery Purchase


Oblique Aerial Imagery


Now that the imagery is available what else can you do with it???Answer: Sketch ValidationSketch vectors exported from CAMA systemGeo-referenced, rotated, and anchored to the structure on the aerial ortho image.GIS sketch layer createdInvalid findings greater than 100 square feet identifiedUsing this process ALL sketches of improvements are validated and can be considered as digitally re-measuredAppraisers work with the validation software to correct any invalid sketches from a queue.Increases accuracy of sketches and adds missing value to the appraisal role.Sketch Validation


Upon completion of the project, the vectors are delivered in a GIS shapefile format.

Manual re-measure estimated cost*:WCAD Improved Properties (2009) = 135,000(x) Re-measured per hour = 6Hours to Re-measure = 22,351 = 10.75 years(x) Avg. Appraiser Salary = $60,000Estimated Cost of Manual Re-Measure =$644,740Gained taxable value needed to recover $644,740 = $28,655,120 * This estimate is only Appraiser Cost (No Entry)

Why Do Sketch Validation?


Sketch Validation Software & Service Cost:WCAD Improved Properties (2009) = 135,000(x) Sketch Validation Cost Per Parcel = $0.43Estimated Sketch Validation Cost = $58,050Gained taxable value needed to recover $58,050 = $2,580,000


Estimated Cost of Manual Re-Measure =$644,740

Estimated Sketch Validation Cost =$58,050

Sketch Validation Results:11% invalid findingsTotal value added to role: $88,530,128Estimated Total Taxes in Year 1: $2,213,253Return on Investment for Year 1 Taxes Gained = $2,213,253Total Cost to District = $135,620ROI = 1632%


Accuracy of the appraisal role with fairness and equality of valuationsAdded value to role that increases tax base by adding missing improvementsCost effective when compared to manual re-measureHuge Return on Investment of monies contributed to your budget by the taxing unitsIncreased credibility


Sketch Validation:Uses sketch vectors currently in your CAMA systemOverlays sketches on most recent aerial photographyEnables correction of invalid sketches efficientlyResulting in accurate sketches

Change Detection:Compares the most recent aerial photograph of an improvement to a previous aerial photographChanges are detected from these photographsDoes NOT correct existing sketch errorsDoes correct missing improvements since last aerial photographSketch Validation Vs. Change Detection


Convert to GIS software most commonly used by your Taxing UnitsPromotes data sharingPurchase aerial ortho and oblique imageryIncreased visibility of improvements Shared use and expense with taxing unitsGeo-Reference (Rectify) your parcels Enables immediate use of your parcel layerCreates a more professional image to your taxing units and the public (increased credibility)Recommended Progression to Assist Taxing Units


Sketch Validation of ImprovementsCreates an accurate sketch of all improvements within CAMA systemChange Detection of ImprovementsContinues accuracy of sketches by detecting changes from each version of your aerial photography

Recommended Progression to Assist Taxing Units


Thank You!Alvin LankfordChief Appraiser

alvinl@wcad.orgPamela OrrDirector of Operations


Williamson Central Appraisal District625 FM 1460Georgetown, Texas78626-8050(512) 930-3787