The District of Columbia

Alley Frontage Lines

Alley Frontage Lines

by Department of Consumer of Regulatory Affairs (DCRA) - Office of the Surveyor (OS) on Weekly

Keywords
About: Property, Land, Location, planningCadastre, Lot, Square
Taking place at: Washington, D.C., District of Columbia, DC, DC GIS, DCGIS

Abstract

Alley Frontage Lines. The dataset contains locations and attributes of alley frontages, created as part of the DC Geographic Information System (DC GIS) for the D.C. Office of the Chief Technology Officer (OCTO) and participating D.C. government agencies.

Please visit http://vpm.dc.gov/ for additional information.

All DC GIS data is stored and exported in Maryland State Plane coordinates NAD 83 meters.

METADATA CONTENT IS IN PROCESS OF VALIDATION AND SUBJECT TO CHANGE.

Purpose

This data is used for the planning and management of Washington, D.C. by local government agencies.

Use constraints

Acknowledgment of the DC Geographic Information Systems Program (DC GIS). The District of Columbia Government makes no claims as to the completeness, accuracy or content of any data contained hereon, and makes no representation of any kind, including, but not limited to, the warranty of the accuracy or fitness for a particular use, nor are any such warranties to be implied or inferred with respect to the information or data furnished herein.

Point of contact

GIS Data Coordinator
in Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington DC, 20001, USA

fax: 202-727-5660
hours: 8:30am - 5:30pm

Credits

Department of Consumer of Regulatory Affairs (DCRA) - Office of the Surveyor (OS), and Office of Tax and Revenue (OTR) - Real Property Tax Administration (RPTA)
Office of Chief Technology Officer (OCTO) - DC GIS

Data accuracy

Accuracy
Validated by source and/or responsible agency

Logical consistency
Vector Property Map QA/QC

1.) Specifications:

Projection Parameters: Coord. System - NAD83, StatePlane, MD, FIPS 1900, meters.
Correct Extent and Mapping Tolerances:
Mapping tolerances implicitly define accuracy and precision of the vector feature datasets.
Min X: 389000, Max X: 408000, Min Y: 124700, Max Y: 147900
Precision: 92563.95 (close to 5 decimals of precision)
Cluster Tolerance: .003048006

2.) QA/QC Steps

Attribute Verification - Database Structure, Domain Values, Field Population
Topological Consistency - Verified Topology against a list of rules, as follows:

Source Checks
Squares were reviewed against their respective source documents (Record Lots- Subdivision Plats, Tax Lots- A&T Plats) and checked for the following:

- Ensure all lots were captured for each square
- Check all lot line dimensions and square footages
- Check for missing building restriction lines on original source plats
- Check for proper lot bearings
- Insure correct units were captured

Squares and Lots Best Fit - Check each squares best fit against the 2002 imagery and ground level features such as curb, sidewalk and buildings.

Errors found during DC QC process were cycled back to vendor until all correction had been completed.

3.) Topology Checks and Rules

ParcelsLn - Must Be Covered By Boundary Of - ParcelsPly
SquaresLn - Must Be Covered By Boundary Of - SquaresPly
TaxLotsLn - Must Be Covered By Boundary Of - TaxLotsPly
RecordLotsLn - Must Be Covered By Boundary Of - RecordLotsPly
ParcelsLn - Must Not Have Dangles
RecordLotsLn - Must Not Have Dangles
SquaresLn - Must Not Have Dangles
TaxLotsLn - Must Not Have Dangles
TaxLotsLn - Must Not Self-Intersect
SquaresLn - Must Not Self-Intersect
RecordLotsLn - Must Not Self-Intersect
ParcelsLn - Must Not Self-Intersect
AlleyLn - Must Not Self-Intersect
TaxLotsLn - Must Be Single Part
SquaresLn - Must Be Single Part
RecordLotsLn - Must Be Single Part
ParcelsLn - Must Be Single Part
AlleyLn - Must Be Single Part
TaxLotsPly - Must Not Overlap
SquaresPly - Must Not Overlap
RecordLotsPly - Must Not Overlap
ParcelsPly - Must Not Overlap
RecordLotsPly - Must Be Covered By - SquaresPly
TaxLotsPly - Boundary Must Be Covered By - TaxLotsLn
SquaresPly - Boundary Must Be Covered By - SquaresLn
RecordLotsPly - Boundary Must Be Covered By - RecordLotsLn
ParcelsPly - Boundary Must Be Covered By - ParcelsLn
TaxLotsPly - Contains Point - TaxLotsPt
SquaresPly - Contains Point - SquaresPt
RecordLotsPly - Contains Point - RecordLotsPt
ParcelsPly - Contains Point - ParcelsPt
TaxLotsPt - Must Be Properly Inside - TaxLotsPly
SquaresPt - Must Be Properly Inside - SquaresPly
RecordLotsPt - Must Be Properly Inside - RecordLotsPly
ParcelsPt - Must Be Properly Inside - ParcelsPly
AlleyLn - Must Be Covered By Feature Class Of - SquaresLn
AlleyLn - Must Be Covered By Boundary Of - SquaresPly

Completeness
Data is mostly complete thru April 2009.

The following issues exist in the property data:

1.) Some squares contain COGO linework entered using degress, minutes, and seconds, as opposed to decimal degrees. This causes spatial inaccuracies that grow as the length of the line gets longer.
2.) Not all Parcels that reside outside of a Square(s) boundary have been processed/created.
3.) Not all Reservations have been processed/created.

Other
1.) Alleys, Building restriction lines, Highway Plans, and Easements are captured if they were on the source material. Source material is active as of November 2002. It is known that not all of these features were captured.
2.) Street width is approximate. Users should rely on the published official street widths to set up property lines or determine right-of-way (this is from the DC Land Surveyors Hand Book). Likewise this should be taking into consideration when doing certain types of GIS analysis utilizing the VP data.
3.) Some Squares are divided by streets. That is, the same Square continues on the other side of the street.
4.) Not all of the fields are currently populated. The remainder of the attribution will be populated once the servers are returned from the vendor containing the source files.
5.) Efforts are being made to bring all layers current.

Horizontal positional accuracy
Since squares are islands and not generated from ground features, staff "best fit" each square to the Earth. Since there is no citywide Survey Coordinate System, squares are placed in their approximate location. Once a square was COGO'ed/created it became a "floating islands" without geographic positioning. Because of this, captured property data had to be positioned relative to other geospatial files that themselves are geo-referenced. Thus, they were fit to the digital ortho's and planimetrics compiled at a scale of 1:100 or 1" ='s 83.3ft.
Squares were visually positioned over the appropriate area in of the orthophoto and planimetrics (ground level feature were primary source).

For the "best fit" to ortho, 95% of features are within 2 meters of their true position on the 2002 orthophoto.

Within a square, the property map relative accuracy is approximately 2 feet.

- Each Square is an Island, alone unto itself.

- Street width is approximate. The published official street widths to set up property lines or determine right-of-way are correct. There is digital scan information available from DDOT regarding Right-of-Way widths.

Vertical positional accuracy
N/A

Lineage / Sources

  • subdivision map
    hardcopy, location
    subdivision maps
    by Department of Consumer and Regulatory Affairs - Office of Surveyor , 2006
  • Assessment and Taxation plats
    hardcopy map, location
    Assessment and Taxation plats
    by Office of the Chief Financial Officer - Real Property Tax Administration, 2006
Lineage / Processes
GIS Data Coordinator
in Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington DC, 20001, USA

fax: 202-727-5660
hours: 8:30am - 5:30pm
-Corrections to some data anomalies

-Approx. 283 of the 800 maintenance transactions completed to bring data current. This equates to the retiring of 614 tax and record lots (these are in the history feature classes) and the creation of 364 new tax and record lots.

- 49 new Parcels

-Updated Maintenance transaction table
GIS Data Coordinator
in Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington DC, 20001, USA

fax: 202-727-5660
hours: 8:30am - 5:30pm
- Appropriations: 10 of the 17 have been captured

- Parcels: 81 new parcels.

- Air Rights Lots: several additional lots retired and captured

- Hundreds of new and retired record and tax lots (retired lots located in history layers)

- Improved best fits around Grant Circle, parkland and railroads.

in OCTO



Recent updates include:

- 122 new tax lots
- 248 new record lots
- 128 new Parcel Lots
- 10 new Air Rights Lots
- Corrections to several data anomalies.
- COL feature class now has all the requested fields from John Codd.
- Moved 16 Squares:

0393
0078
3113
1832
2850
1067
1080
5598
5999N
1300
3189
1065
1859
1815
1321
1292
Retiring of 25 Alley Frontages
Retiring of 7 Alley Frontages
Retiring of 1 Alley Frontage
Retiring of 4 Alley Frontage

Distribution

Most DC GIS datasets can be downloaded from "http://dcgis.dc.gov" on the data center page. Orders can also be made by contacting OCTO GIS at "dcgis@dc.gov", especially for datasets not available for download.

Distribution liability
Acknowledgment of the DC Geographic Information Systems Program (DC GIS). The District of Columbia Government makes no claims as to the completeness, accuracy or content of any data contained hereon, and makes no representation of any kind, including, but not limited to, the warranty of the accuracy or fitness for a particular use, nor are any such warranties to be implied or inferred with respect to the information or data furnished herein.

Distributed by
GIS Data Coordinator
in DC Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington DC, 20001, USA

fax: (202) 727-5660
hours: 8:30 am - 5:30 pm

Entity

AlleyLN

Attributes

  • NARRATIVE
    This attribute stores general comments about the feature.
  • ALLEYPLYID / ESRI
    Internal feature number.
  • SHAPE_LEN / ESRI
    Internal feature number.
  • ALLEY_NAME / ESRI
    Internal feature number.
  • STATUS
    The status value is always set to 1 which is the only value in the STATUS_CURRENT coded value domain. The value of this attribute is constant for a class. It denotes whether the information is considered current or historical. This attribute is primarily used by applications.
    • 1 / Feature is part of active layer
    •  
  • SQUARE
    Square value from the SSL identifier.
  • CREATION_D
  • RECORDATIO
  • SUFFIX
    Suffix value from the SSL identifier.
  • EXPIRATION
  • GIS_ID
    OCTO GIS Identifier
  • SHAPE / ESRI
    Feature geometry.
  • RECORD_LEN
  • RECORD_BEA
  • RECORD_B_1
  • RECORD_SPI
  • RECORD_S_1
  • RECORD_ARC
  • RECORD_DEL
  • RECORD_RAD
  • RECORD_MSL
  • SURVEYED_L
  • SURVEYED_B
  • SURVEYED_1
  • SURVEYED_D
  • SURVEYED_R
  • COMPUTED_L
  • COMPUTED_B
  • COMPUTED_1
  • COMPUTED_D
  • COMPUTED_A
  • COMPUTED_R
  • LINE_CLASS / ESRI
    Feature geometry.
  • Shape / ESRI
    Feature geometry
  • KILL_DT
  • NAMED_ALLE
  • ALLEYLNID

Entity

VPM_OWNER.AlleyPLYHaveAlleyLN

Attributes

































Metadata

FGDC Content Standards for Digital Geospatial Metadata / FGDC-STD-001-1998 as of 20121011

Provided by
GIS Data Coordinator
in D.C. Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington DC, 20001, USA

fax: (202) 727-5660
hours: 8:30 am - 5 pm