The District of Columbia

Mass Points

Mass Points

by Office of the Chief Technology Officer on 12/02/2009

Keywords
About: Terrain, elevation, topography, contour, breakline
Taking place at: Washington, D.C., District of Columbia, DC, DC GIS, DCGIS

Abstract

Mass Points. The dataset contains DTM masspoints derived photogrammetrically to support 2’ contours. Masspoints and breaklines were compiled from Spring 2008 aerial photography using softcopy photogrammetric techniques. Masspoint elevations are in based on NAVD US feet.

Masspoints and breaklines were compiled to support generation of a TIN and the subsequent processing of 2’ contours. All DC GIS data is stored and exported in Maryland State Plane coordinates NAD 83 meters for horizontal locations.
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 DC Office of the Chief Technology Officer (OCTO)

801 7th Street SW
Washington DC , 20024, USA

phone: (202) 727-5660
hours: 8:30 am - 5:00 pm

Credits

Office of the Chief Technology Officer

Data accuracy

Accuracy
Validated by source and/or responsible agency.

Logical consistency
Validated by KCI Technologies, Inc. and OCTO. OCTO developed and operated a QA/QC program to check the deliverables. Generally, the program consists of various types of processes grouped into visual checks, automated procedures, edge-matching routines, and specialized checks. Staff identified issues in a shapfile with appropriate descriptions for the vendor to fix. The data was delivered in preliminary format for a thorough review and identification of issues. The vendor fixed the data and delivered final data which OCTO checked to ensure the vendor made the fixes appropriately.

Completeness
Data believed to be complete and accurate, subject to change. Validated by responsible agency

Horizontal positional accuracy
Horizontal Accuracy data points is in accordance with ASPRS Class I Accuracy standards for 1"=100' scale mapping.

Vertical positional accuracy
This data has been tested in accordance with the NSSDA Spatial Data Standards. Fifty-seven (57) checkpoints were used in the evaluation. Checkpoints were derived from multiple sources including: 1) KCI surveyed independent checkpoints, 2) Checkpoints/GCPs used for a previous mapping program (14th street bridge), 3) Survey control withheld from the final aerial triangulation solution All of these tests were based on a final Airborne GPS, AT, and DTM. As a result the data has been found to have a vertical RMSE of 1.0ft. At the 95% confidence level this is 2.0ft. This data has been found to meet ASPRS Class 1.5 Accuracy Standards. In comparison to National Map Accuracy Standards where 90% of the checkpoints should be within 1’ our findings indicate 86% of the well defined points are within 1’ and the remaining 93% are within 2’. Any accuracy limitations were primarily impacted by flying height, image resolution, and lack of sidelap in specific areas which impacts the overall block adjustment.

The breakline and masspoints are good for planning purposes but should not be used for precise engineering and survey work at the ASPRS class 1 accuracy standard level.

Lineage / Sources

  • <The title or descriptor of the source.>
    filmstrip, New aerial photography was collected in the Spring of 2008 to support new orthoimagery and planimetric updates. This aerial photography was composed of approximately 52 flight lines and a total of 1552 exposures.. The mission was flown with one Vecxel Ultracam X camera and collected ABGPS and IMU for each exposure.
    aerial photography
    by <The name of the organization or individual that developed the source.>, <The publication date of the source. This is formatted to "dd/mm/yyyy.">
Lineage / Processes

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

DCGIS.MassPt

Attributes

  • Shape / ESRI
    Feature geometry
  • OBJECTID / ESRI
    Internal feature number.
  • SHAPE / ESRI
    Feature geometry.
  • ELEVATION
    Elevation value in feet

Metadata

FGDC Content Standards for Digital Geospatial Metadata / FGDC-STD-001-1998 as of 12/05/2009

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