| Description | |||
| Abstract: Represents locations/lines of equal elevation. These 2 foot contours were produced as part of the VGIN mapping project executed in 2007. (Note: Although the contract with VGIN (VA Geographic Information Network) was initated in 2006, due to the late signing of the contact between the State and their contractor, there was not a long-enough "leaf-off" period to complete state-wide orthophotograhy mapping; the City of Richmond was one of many localities postponed until the Winter of 2007.) | |||
| Purpose: The creation of the contour data was executed to capture the existing ground conditions at a specific point in time for the purpose of GIS mapping and analysis. Contour information is used for plannimetric mapping and for creating TINs and RASTERs, which support 3D mapping and ground/slope visualization. TINs and RASTERs of elevation data support spatial analyses related to slopes, viewsheds, water runoff, and other map algebra-based applications. | |||
| Supplemental Information: Contours 2007: still considered part of the City's planimetric base mapping, these contours were obtained via the "VA Base Mapping Project (VBMP)." The City contracted in 2006-07 to upgrade the VA Geographic Information Network (VGIN) orthophotography VBMP product from 1 foot resolution to 6 inch resolution, and additionally contracted to have 2 foot resolution contours developed. The analog aerial photography was collected at 1"=200' scale and flown in Winter 2007. The aerial photography was controlled with strategic photo-identifiable ground control points. The ground control points were referenced to a Statewide adjusted Network in North American Datum 1983; Virginia State Plane South. The film was scanned at 14 microns and the aerotriangulation was executed using Zeiss ISAT software. The accuracy of the aerotriangulation data supports 1"=100' mapping and the generation of 2' contours. The Digital Terrain Model (DTM) and subsequent Triangular Irregular Network (TIN) used to the interpolate the contours was photogrammetrically stereo-compiled using fully manual methods to collect masspoints and breaklines. The data was initially compiled in tile (2,500' X 2,500') tile format and seamlessly merged together into GeoDatabase format for final delivery. Variations existing between the contour datasests (1999 vs. 2007) is not uncommon. Photogrammetry is not an exact science; scale, resolution and interpretation play a large role in the data output. Sanborn wrote: "Contours are lines of continuous elevation however, the methodology for contour generation and particularly "smoothing" of the contours are aesthetic in nature and subjective to the cartographer creating and editing the contours. Although both the City's 1999 and 2007 contour datasets were photogrammetrically derived, the software utilized to create the contours and smoothing routines have changed substantially from 1999 to 2007. In essence, the less smooth the contour, the more accurate it depicts the terrain. In the 2007 product, Sanborn applied minimal smoothing routines to minimize any distortion. Overall, the 2007 contour dataset is a better source to use given it was produced using more current techniques and minimal smoothing." Other than a site survey, nothing is going to be truly accurate. | |||
| Contact | |||
| Custodian: | Pravin Mathur | ||
| Department: | Public Works | ||
| Position: | GIS\Cityworks Manager | ||
| Address: | 900 E Broad St, 7th Floor | ||
| City: | Richmond | ||
| State: | Virginia | ||
| Zip Code: | 23219 | ||
| Email: | Pravin.Mathur@richmondgov.com | ||
| Time Period of Content | |||
| Date: | Winter 2007 | ||
| Status | |||
| Progress: | Complete | ||
| Update Frequency: | None planned | ||
| Spatial Domain | |||
| West Coordinate: | -77.614486 | ||
| East Coordinate: | -77.370922 | ||
| North Coordinate: | 37.604870 | ||
| South Coordinate: | 37.438044 | ||
| Spatial Data Information | |||
| Data Type: | vector digital data | ||
| Data Format: | SDE Feature Class | ||
| Data Projection: | Lambert Conformal Conic | ||
| Access and Usage Information | |||
| Access Constraints: | none | ||
| Use Constraints: | All GIS layers and datasets are owned by the City of Richmond and can not be modified, re-distributed, and/or re-sold without a sub-licensing agreement. All guarantees of validity expire once a dataset leaves the City of Richmond firewall or physical premises. Acknowledgement of the City of Richmond GIS would be appreciated in products derived from these data. | ||
| Entity and Attribute Information | |||
| Entity Name: | vector.ric.base_Contour2007 | ||
| Entity Type: | Feature Class | ||
| Entity Count: | 85059 | ||