When Domains Collide:When Domains Collide: Linking Databases to Linking Databases to
Determine Pupil Generation Determine Pupil Generation RatesRates
Jessica GormontJessica Gormont, Jefferson County GIS/Addressing Office, Jefferson County GIS/Addressing Office
Tori MyersTori Myers, Jefferson County Assessor’s Office, Jefferson County Assessor’s Office
Mark SchiavoneMark Schiavone, Jefferson County Department of Capital Planning and , Jefferson County Department of Capital Planning and
ManagementManagement
School Impact Fee
Fee levied against new residential construction
Calculated to ensure capacity expansion
School Impact Fee
Impact Fee = ( Cost - Credit ) x Demand Generator
Asset value per student
Non-impact fee revenue per
student
Students per residential unit
Pupil Generation Rate:The number of school-aged children, usually expressed as level of schooling, per household.
Traditionally Determined:
•Using Census/PUMS data
•Local census/sampling
Current Status: Jefferson County
Pupil Generation data linked to Housing Unit Type: Single Family Detached (includes
manufactured homes) Townhome/Duplex Multifamily Apartment
Example: Miami-Dade County
0
0.1
0.2
0.3
0.4
0.5
0.6
800 1000 1200 1400 1600 1800 2000 2200 2400 2600 3000
Pupil Generation Rates vs. Housing Unit Size (idealized)
Board of Education Transportation DatabaseBoard of Education Transportation Database
•Highly granular: pupil generation per address •Lacks information about housing unit type or size
Assessor’s DatabaseAssessor’s Database
•Highly granular: Housing unit type and size •Addresses not accurate – Parcel_ID highly accurate
How to Link?How to Link?
BOE data(good addresses)
Assessor data(good map/parcel)County
GIS
Link addresses to addresses
Link parcel_id to parcel_id
The PlanThe Plan
Analyze BOE data and cleanAnalyze BOE data and clean Pass BOE data to GIS for joinPass BOE data to GIS for join GIS pass data to Assessor to add GIS pass data to Assessor to add
building databuilding data Deliver combined dataset to Deliver combined dataset to
consultant for analysisconsultant for analysis
Preliminary DataPreliminary Data
Original parcel layer created in 2009Original parcel layer created in 2009 IAS queries for tax code dataIAS queries for tax code data
Finding Residential Finding Residential AddressesAddresses
Spatial Join - address points & Spatial Join - address points & parcel polygonsparcel polygons added Parcel ID to pointsadded Parcel ID to points
Tabular Join - address points & IAS Tabular Join - address points & IAS datadata added tax codes to address pointsadded tax codes to address points
Adding BOE DataAdding BOE Data Tabular Join - BOE data & address Tabular Join - BOE data & address
pointspoints Loss of 12.5%Loss of 12.5% Loss caused by variety of errorsLoss caused by variety of errors
Secondary Visual Clean Up of BOE dataSecondary Visual Clean Up of BOE data
Second Tabular Join of BOE dataSecond Tabular Join of BOE data loss of 10% - deemed acceptableloss of 10% - deemed acceptable
Adding Additional Adding Additional InformationInformation
Decided to add secondary information Decided to add secondary information in case needed by contractorin case needed by contractor
Spatial Join to Jurisdiction layerSpatial Join to Jurisdiction layer Allowed for removal of address points Allowed for removal of address points
within towns if necessarywithin towns if necessary
Spatial Join to Subdivision/MHP layerSpatial Join to Subdivision/MHP layer Allowed for separation of Mobile Homes in Allowed for separation of Mobile Homes in
MHPsMHPs
Final DataFinal Data
Data received from GISData received from GIS Several queries to retrieve data for Several queries to retrieve data for
Living unit size and number of Living unit size and number of bedrooms.bedrooms.
Final DataFinal Data Final data sent to contractor Final data sent to contractor
contained:contained: Physical Location AddressPhysical Location Address Parcel IDParcel ID Tax CodeTax Code Number of School Kids by Grade LevelNumber of School Kids by Grade Level Building Assessment DataBuilding Assessment Data JurisdictionJurisdiction Subdivision/MHP nameSubdivision/MHP name
ResultsResults2000 Census Housing Units % Housing P/HH Elementary Middle HighSingle Family 14340 0.89 0.50 0.14 0.12 0.24 Duplex 277 0.02 0.38 0.11 0.09 0.18 Multifamily 1541 0.10 0.28 0.08 0.07 0.13 Total 16158 1
•Original census data from 2000•Only 3 housing unit types recognized•No further granularity
ResultsResultsSize Range Square Feet* Pupils/Unit**
0-1,000 816 0.111,001-2,000 1,469 0.152,001-3,000 2,419 0.213,001-4,000 3,409 0.284,001+ 4,730 0.28
All Single Family Units 0.18
* Source: Jefferson County Assessor's Office.** Source: Jefferson County Schools.
Actual Averages
y = 0.1075ln(x) - 0.6174R² = 0.9509
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0 1,000 2,000 3,000 4,000 5,000
Stud
ents
Square Feet
Elementary School Students per Single Family Detached Unit
Actual Averages Trend Analysis Log. (Actual Averages)
ResultsResultsSize Range Square Feet* Pupils/Unit**
0-1,000 816 0.051,001-2,000 1,469 0.072,001-3,000 2,419 0.093,001-4,000 3,409 0.134,001+ 4,730 0.11
All Single Family Units 0.08
* Source: Jefferson County Assessor's Office.** Source: Jefferson County Schools.
Actual Averages
y = 0.0425ln(x) - 0.2376R² = 0.8646
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0 1,000 2,000 3,000 4,000 5,000
Stud
ents
Square Feet
Middle School Students per Single Family Detached Unit
Actual Averages Trend Analysis Log. (Actual Averages)
ResultsResultsSize Range Square Feet* Pupils/Unit**
0-1,000 816 0.061,001-2,000 1,469 0.092,001-3,000 2,419 0.133,001-4,000 3,409 0.164,001+ 4,730 0.17
All Single Family Units 0.11
* Source: Jefferson County Assessor's Office.** Source: Jefferson County Schools.
Actual Averages
y = 0.0672ln(x) - 0.3962R² = 0.9923
0.000.020.040.060.080.100.120.140.160.180.20
0 1,000 2,000 3,000 4,000 5,000
Stud
ents
Square Feet
High School Students per Single Family Detached Unit
Actual Averages Trend Analysis Log. (Actual Averages)
ResultsResultsType of Size Elem. School Middle School High School Total
Housing Unit Thresholds (sq ft) Rate Rate Rate RateSingle Family
0 -1,500 0.17 0.07 0.10 0.341,501 - 2,500 0.22 0.09 0.13 0.452,501-3,500 0.26 0.11 0.15 0.523,501 + 0.29 0.12 0.17 0.58
Townhouse1 0.11 0.04 0.05 0.19
Multi-family2 0.08 0.02 0.03 0.14Mobile Home 0.15 0.06 0.09 0.30
1. Includes single family attached and duplexes.2. Includes 3 units or more.
ConclusionConclusion
Multiple databases linked with no Multiple databases linked with no loss of fidelityloss of fidelity
GIS datasets are rich and merge well GIS datasets are rich and merge well with other domainswith other domains
Agencies able to create sophisticated Agencies able to create sophisticated studies at low coststudies at low cost