Land Details Bridging the Gap between Assessor Acres and GIS Acres
What are Assessor Acres? It is a legally agreed upon approximation of size Applies to larger parcels Has deep historical roots. Thomas Jefferson
GIS vs Assessor Acres Assessor Acres Legally defined area Fixed area Absolute precision Users: Legislature Assessors Planners Citizens
GIS Acres vs Assessor Acres GIS Acres Assumes the world is flat Measurable accuracy in x and y Area changes to accommodate spatial accuracy Users: GIS
Common Misconceptions GIS area is more accurate GIS Area is different Using GIS area would make things easier Legal areas are fixed GIS polygons are not fixed size
Analogous to a Linear Reference System (LRS) An LRS route can have user defined length Events are placed with respect to the defined length. A Parcel can have a user defined area Sub polygons can be mapped with respect to the defined Area
Assessor Acres Applications Current Use Application Areas Assessor Easements Senior Exemptions One Acre Homesites Market Value Calculations Automated Splits/Merges
Sample Parcel 1 Acre Homesize.55 Acre Natural Gas Easement 14.25 Acre Current Use Application 15.80 Total Assessor Acres 15.277 Total GIS Acres Factor: 15.80 / 15.277 = 1.0342
Land Detail Layer Sample Parcel
Mapping in Assessor Acres Homesite Area: 42122.63 * 1.034212 = 43560
Land Detail Market Value Layer Based on: Slope, Wetlands, Easements, Homesite
Market Value Calculation GIS Acres * Factor * Market Value Type Rate Per Acre
Current Use Value Layer Based On Soil Types
Current Use Value Calculation GIS Area * Factor * Soil type Rate Per acre
Appraisers Role Interface between Policy and Public Did you take my wetland, cliff, easement into consideration?
Appraiser / Public Generalizations Slopes Includes Low or wetland Easements May not be a recorded easement. Areas Approximate but set in stone
Easements: Easements
Old School: 2 Sets of books Maintained Manually Totals Must Balance Easements, Wetlands deducted from Flat or Rolling
Mapping Benefits Easements No longer lost in the database Can visualize errors, inconsistencies No longer automatically deducted from high value land Slopes and Soils can use GIS Lidar Wetlands Inventory/Model
GIS Mapping Challenges How do you create polygons of a predefined size? Real Time Layer Maintenance In synch with Assessors Database Acreage adjustments Easement Add/Drops In synch with GIS Parcels Layer Parcel edits: Fitting new subdivisions In synch with Current Use Layer
Editing Land Details Place a seed feature: Point, Line, Poly Grow the feature to the correct size Adjust other features to accommodate the new polygon.
Homesite Seed
New 1 Acre Homesite
Easement Seed 2.5 Acre Easement
New Easement Homesite moved
Maintenance Parcel Splits and Merges Boundary Line Adjustments Assessor Acreage Correction Add, Drop, edit of easements
Requirements Keep layers in synch with Assessor database Keep Assessor database in synch with layers Keep it simple
Land Detail Worksheet
Assessor Database GIS Layer
Split Merge
LandDetail Wizard Summary Spreadsheet / Wizard interface Automatically applies most changes to map layers Updates GIS Layers Land Detail Land Detail Market Value Current Use Value Updates Assessor s Database
Current Use Mapping based on tree lines, fields Acreage based on application Applications persist when parcels are split One Parcel can have multiple applications One Application can include multiple parcels
Conclusions Mapping by area is pretty cool Presents new ways of viewing information Simplifies, standardizes, automates many Assessment tasks Bridges the gap between legal areas and GIS based areas