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