2 foot contours. This dataset contains locations and attributes of 2-ft interval topography data, 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. In addition to the 2-ft contour data ancillary datasets containing an ESRI geodatabase of masspoints and breaklines and a TIN (Triangulated Irregular Network) have also been provided and are an integral part of this dataset. 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.
This data is used for the planning and management of Washington, D.C. by local government agencies.
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.
801 7th Street SW
Office of the Chief Technology Officer
Contours were coded as either intermediate or index depending on the elevation attached to each contour. The tiled contours are then processed along with additional data such as buildings so that indefinite or hidden contours can be properly coded.
Validated by KCI Technologies, Inc. and OCTO. Contours were checked for overlaps or dangles. Any errors that may be flagged are corrected by a GIS technician. Tiles of data are also checked to ensure that contour ties between tiles are spatially connected and have like attributes. If any errors are found they are corrected by a GIS technician. Contours are checked for proper connectivity and topology by using various ESRI tools.
Data believed to be complete and accurate, subject to change. Validated by responsible agency"
Horizontal Accuracy of planimetric/topographic data is in accordance with ASPRS Class I Accuracy standards.
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 contours are good for planning purposes but should not be used for precise engineering and survey work at the ASPRS class 1 accuracy standard level.
attributes and location
A photogrammetrically compiled DTM of masspoints and breaklines was compiled using ZI Imaging softcopy photogrammetric workstations. The completed DTM dataset, having already been checked for accuracy, was run through the Sanborn's APS proprietary software in order to generate contours. All DTM data is translated into APS format. Tiles of overlapping DTM data are extracted in order to make contour processing more efficient. The overlapping of DTM data allows for contour generation to be more precise at tile edges. Contours were generated at a 2' interval for each tile of data. During the generation process, elevation attributes were created on each contour. Any enclosed contour that was less than 30 square meters in area was automatically deleted. Contours were then coded as either intermediate or index depending on the elevation attached to each contour. Contours are also gently smoothed and/or filtered in order to give a more aesthetically pleasing look. As part of Sanborn's quality process, the contours were checked for overlaps or dangles. Any errors that may be flagged are corrected by a GIS technician. The tiled contours are then processed along with additional data such as buildings so that indefinite or hidden contours can be properly coded. At this point, tiles of data are also checked to ensure that contour ties between tiles are spatially connected and have like attributes. If any errors are found, they are corrected by a GIS technician. Once the contours are deemed complete, they are translated out of APS format into an ESRI geodatabase as a single feature class. The contours are checked again for proper connectivity and topology by using various ESRI topology and visual tools. Once these checks are finished, the data is considered complete. DTM data also was exported to a ESRI TIN prior to delivery. Data was delivered to KCI for visual inspection and corrections were ideintified and data was reprocessed and redelivered as appropriate.
1935 Jamboree Drive Suite 100
OCTO GIS Internal Identifier
441 4th St NW, Suite 930 South
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 "email@example.com", especially for datasets not available for download.
441 4th St NW, Suite 930 South