TOB June 12, 1999

Andrew Flora

TIGER Operations BranchGeography Division

U S C E N S U S B U R E A UHelping You Make Informed Decisions

ZIP Code Tabulation Areas For Census 2000

NCHS, CDC

June 13, 2000

TOB June 12, 1999

.... are generalized area representations of United States Postal Service ZIP Codes developed by the U.S. Census Bureau for tabulating statistical data.

ZIP Code Tabulations Areas (ZCTAs™)

ZCTA™ is a trademark of the U.S. Census Bureau

Select South Carolina Dress Rehearsal Counties

1999 South Carolina ZIP Code TabulationAreas for select Dress Rehearsal Counties

29715

297042973029742

2903129706

29729

29720

2971829175

2906729058

29009

2903229020

290HH29074

291HH

29130

29180

29014

29055

29132

290HH

29015

29036

290HH 2921229210

292042920529201 29209

29061

29052

29044

290

29128

290782901029045

292292901629075

2906329203 29223

292

29206

29065

297HH29714

29712

5 0 5 10 Miles

TOB June 12, 1999

.... are distinct from other area representations of ZIP Codes because they reflect address locations and ZIP Codes collected or verified during Census 2000 field operations.

ZCTAs

TOB June 12, 1999

.... are distinct from statistical areas such as census tracts because they are not stable over time and they are computer delineated using addresses rather than formally delineated before the census.

ZCTAs

Census 2000 Dress Rehearsal Population DensitySacramento, CA Dress Rehearsal Site

Map Prepared byTIGER Operations Branch

Geography DivisionU.S. Bureau of the Census

1999

Population / square mile< 602602 - 18481849 - 43864387 - 6454> 6454

Comparison of Statistical Entities

Census Tracts ZIP Code Tabulation Areas (ZCTA)

TOB June 12, 1999

Census Tracts ZCTAs

Comparisons

• Locally defined • Generally stable/comparable over time • Ideally 1500 housing units• Boundaries follow features• Nest within counties/county county equivalents

• Defined by addresses and extension algorithms • Boundaries and codes change over time • Variable size• Boundaries follow tabulation block boundaries• Cross counties but not states

TOB June 12, 1999

• New for Census 2000• Product and trademark of the US Census Bureau• Prototype ZCTAs released with Census 2000 Dress Rehearsal products• Documentation is available on the web:

http://www.census.gov/geo/ZCTA/zcta.html

Introducing ZCTAs!

TOB June 12, 1999

• Assign a ZCTA code to all land areas• Follow census block boundaries • Assign a single ZCTA code to each block • Use a fully automated process• Match true ZIP Codes as closely as possible

Requirements for Building ZCTAs

TOB June 12, 1999

• Represent the majority ZIP Code of the addresses in a census block• Represent a USPS 5- or 3-digit ZIP Code• Exclude unique, single delivery point ZIP Codes for firms and organizations• Include dedicated P.O. Box ZIP Codes In rural areas

ZCTA Codes

TOB June 12, 1999

• 5-digit numeric ZCTA codes 22301 (land & internal water) • Generic 3-digit ZCTA codes 223XX (land & internal water) 223HH (water along margins of several land ZCTAs )

ZCTA Codes

TOB June 12, 1999

• Addresses with incorrect or out-dated ZIP Codes • Blocks split between ZIP Codes• Areas with no addresses or ZIP Codes

Challenges for Delineating ZCTAs

TOB June 12, 1999

ZIP Codes follow the street network

ZIP Code Delivery Routes

Addresses with ZIP Code A

Addresses with ZIP Code B

TOB June 12, 1999

Determine majority ZIP Code of available addresses

ZCTAs Reflect Majority ZIP

ZCTA representing ZIP Code A

ZCTA representing ZIP Code B

TOB June 12, 1999

Addresses with P.O. Box ZIP Codes scattered among addresses with city style delivery

P.O. Box ZIP Codes

Addresses with ZIP Code A

Addresses with P.O. Box ZIP Code B

P

TOB June 12, 1999

P.O. Box ZIP Codes in areas with city style deliveryare excluded from becoming ZCTAs.

P.O. Box ZIP Codes

ZCTA representing ZIP Code A

P.O. Box ZIP Code B is excluded

P

X

TOB June 12, 1999

Addresses with P.O. Box ZIP Codes clusteredaround post office in rural delivery areas

P.O. Box ZIP Codes

Addresses with ZIP Code AAddresses with P.O. Box ZIP Code B

P

TOB June 12, 1999

P.O. Box ZIP Codes in rural delivery areas may become ZCTAs

P.O. Box ZCTA

ZCTA representing ZIP Code AZCTA representing P.O. Box ZIP Code B

P

Types of Unassigned AreaBetween

ZIP Code Tabulation Areas (ZCTAs)

Internal Coverage Holes Coverage Gaps BetweenZCTAs

Fringe Areas and “Islands” Sparsely Settled Areas

• waterway• park lands• industrial areas• undeveloped lands

• waterway• park lands• industrial areas• undeveloped lands

Islands surrounded by coastal or inland waterways.

Residential/commercial areas on the edge of:

• farm land• public lands• large industrial or mining areas• undeveloped wetlands

Sparsely located homesteads or small population centers in rural areas characterized by:

• farming• ranch land• mining• forest land• wilderness areas

12345

12345

12346

12347

12346

12345

12347

12346

12345

Internal Coverage Holes Within ZIP CodeTabulation Areas (ZCTAs)

• waterway• park lands• industrial areas• undeveloped lands

12347

Internal Coverage Holes Within ZIP CodeTabulation Areas (ZCTAs)

Extend the surrounding ZCTA to fill “holes” within the coverage.

12347

12345

12346

12347

Coverage Gaps Between ZIP Code TabulationAreas (ZCTAs)

• waterway• park lands• industrial areas• undeveloped lands

12345

Coverage Gaps Between ZIP Code TabulationAreas (ZCTAs)

Grow ZCTAs outward to fill adjacent blocks until all gaps are filled.

Assign special 3-digit water ZCTA codes to water features on the margins.

12346

12347

123HH

Unassigned Fringe Areas and “Islands”ZIP Code Tabulation Areas (ZCTAs)

Islands surrounded by coastal or inland waterways.

Residential/commercial areas on the edge of:

• farm land• public lands• large industrial or mining areas• undeveloped wetlands

12346

12345

12347

Unassigned Fringe Areas and “Islands”ZIP Code Tabulation Areas (ZCTAs)

Fill unassigned blocks on the edge of ZCTAs with adjacent ZCTA code.

Fill islands with the ZCTA code of nearby land areas.

Assign a generic 3-digit ZCTA code to large unassigned land areas on the fringes of existing assigned areas.

12346

12345

12347

123XX

123HH

Fragmented ZIP Code Tabulation Areas(ZCTAs) in Sparsely Settled Areas

12346

12345

Dispersed homesteads or small population centers in rural areas characterized by:

• farming • forest land• ranch land • wilderness areas• mining

123XX

TOB June 12, 1999

• Validate ZCTA Code in fragments • Add blocks along road network to bridge fragments• Respect natural and cultural boundaries• Fill in small enclaves and “cavities”• Leave remaining area as a generic ZCTA

Rural Fragments

Fragmented ZIP Code Tabulation Areas(ZCTAs) in Sparsely Settled Areas

12346

12345

Assign ZCTA codes to “windows” that enclose the ZCTA fragments. The balance of the area receives a generic 3-digit ZCTA code.

123XX

95824

95815

95835 95673

95660

95821 95841

95825

95864958199581695814

9581895817

9582095826

958299582895823

95758

95832

95831

95822

95838

95833

95834

Areas with no MAF addresses appear in white.

Initial ZIP Code Tabulation AreasSacramento, CA Dress Rehearsal Area

3 Miles0 1 2

ZIP Code Tabulation AreasSacramento, CA Dress Rehearsal Area

95835 95673

95660

9582195841

958259586495819

9581695814

958HH

9581895817

95820 95826

95829

95828

95823

95758

95832

95831

95822

95824

95838

95833

95815

95834

3 Miles0 1 2

54150

54135

54174

54124

Areas with no MAF addresses appear in white.

Initial ZIP Code Tabulation AreasMenominee, WI Dress Rehearsal Area

0 3 6 Miles

541

54150

54135

541HH54124

54174

ZIP Code Tabulation AreasMenominee, WI Dress Rehearsal Area

0 3 6 Miles

TOB June 12, 1999

• Monitor ZIP Code changes from USPS sources (ZIPMOVE file)

• Monitor changes in summary statistics

ZCTA Maintenance

TOB June 12, 1999

• Create new MAF extract with - Latest ZIP Codes - New addresses

• Match addresses and ZIP Codes to ZCTA assignments block by block

• Identify negative changes in match rates

ZCTA Summary Statistics

0 - 250250 -750

750 -1500

1500 -2500

2500 -5000

5000 -10000

10000-

15000

15000-

20000

Number of MAF Addresses per ZCTA

70

80

90

100

Percent of addresses whereZIP Code equalsZCTA

ZCTA Match Rates by Number of MAF AddressesSouth Carolina Dress Rehearsal Area