IowaGeospatialInfrastructure爱荷华市地理空间基础设施.doc

Status of Framework Layers in Iowa September 2008 1) Geodetic Control FGDC Description: Geodetic control provides a common reference system for establishing the coordinate positions of all geographic data. It provides the means for tying all geographic features to common, nationally used horizontal and vertical coordinate systems. The main features of geodetic control information are geodetic control stations. These monumented points (or in some cases active Global Positioning System control stations) have precisely measured horizontal or vertical locations and are used as a basis for determining the positions of other points. The geodetic control component of the framework consists of geodetic control stations and related information -- the name, feature identification code, latitude and longitude, orthometric height, and ellipsoid height, and metadata for each station. The metadata for each geodetic control point contains descriptive data, positional accuracy, condition, and other pertinent characteristics for that point. Geodetic control information plays a crucial role in developing all framework data and users applications data, because it provides the spatial reference source to register all other spatial data. In addition, geodetic control information may be used to plan surveys, assess data quality, plan data collection and conversion, and fit new areas of data into existing coverages. Current status: There are 6597 (142 HARN) NGS control points in Iowa (retrieved summer 2006 from NGS database), 1757 of them having been visited in the last 20 years by NGS. There are 142 HARN control points in Iowa (retrieved summer 2006 from NGS database) About 60 counties in Iowa have GPS control surveys. Some are available to the public through real estate web mapping applications or the ICIT data repository  HYPERLINK / /. There are pdf files containing information on USGS benchmarks, but no GIS coverage showing their approximate locations. Table 1: Description of