Geographic Information Systems
Metadata
Metadata is data about data, or information about information. Confused? Don't worry, so is everyone else.
When working with map files, database, and other types of information, it is very important to know where the information came from, how it was produced, what format it's in, its accuracy, its scale, its orientation, its coordinate system, and much, much more. The best way to let a user know all of this information is to attach a Meta Data file that has information that is considered standard need to know by the federal and state governments.
Metadata is currently being produced for all GIS datasets.
CURRENT ARCGIS DATASETS - 2004 - TO PRESENT:
2001 - March - Digital orthophotography was flown and produced by Kimball and Associates, in a NAD83 State Plane Virginia North projection. The ortho data set is broken down into 542 tiles.
2002 - Planimetric Production Phase I - Planimetric data set produced from 2001 digital orthophotos via photogrammetrics by SDC. Data set included roads, buildings, natural features, hygrography, and manmade features.
2003 - Planimetric Production Phase II - completion of hypsography (contours and topography) created for entire county at 25 foot and 5 foot intervals. (SDC)
2004 - Planimetric Production Phase III - completion of parcel and tax mapping data digitized and "rubber-sheeted" to match planimetric data.
Currently the GIS staff are working at updating the planimetric datasets, populating tabular information, and generating metadata for all.
DATA PRIOR TO 2003:
- In 1986, Frederick County embarked on an E-911 project. From 1986 to 1989 all of the state maintained roads and private roads with four or more addressable structures was names.
- Next a consultant was hired to produce a set of AutoCAD digital maps based on the County's tax map base using the state plane coordinate system. To accomplish this, the consultant digitized or drew digital maps of the 15 U.S.G.S. quadrangles that cover the county. For such a small area, compared to the world that is, the quadrangle grid and the state plane grid match fairly well. U.S.G.S. quads were the 7.5 minute series that have a scale of 1"=2000' , a NAD 27 map projection, and an accuracy of about 50 meters on the ground. These quads were then broken down into 9 rectangles each matching the tax map grid with a map scale of 1"=600 feet
- With the base map in place, the parcel information from the tax maps was "rubber-sheeted" or made to fit using regular aerial photography shot at the same scale.
- Additional information such as rural landmarks, wetlands, flood plains, etc., have been digitized into these base maps and then exported to a separate file with the same map criteria.
- And then from 1990 to 1995 this information was converted from a CAD format to a GIS format using ESRI software such as ArcCAD, ArcView, and ArcInfo. Coverages and shape files were fleshed out by adding new fields and records to the various databases.
- Data Processing exports the CAMRA or parcel information file out to a database format, daily.
- Digital data is maintained on a daily basis and improved as needed. GIS products are produced as close to release date to make sure that any information going out is as current as possible.
