DCW Data Description
Data Sources | Arc Densification | Edgematching | Data Quality
Data Sources
The DCW data is derived primarily from the US Defense Mapping Agency Operational Navigation Charc (ONC) series (1:1,000,000 scale). Data for the Antarctic region were filled in with Jet Navigation Charts. Several additional sources have been used to complete the data set. They include, among others, the DMA's Digital Aeronautical Flight Information File, Advanced Very Hight Resolution Rediometer data.
The ONC data was designed to aid navigation of pilots flying at low and medium altitudes, preparation of cockpit displays, and to support military planning. They may or may not be suitable for other purposes.
The data is in a geographic, or latitude and longitude, coordinate system.
Arc Densification
The arcs in the database were densified so that there was at least one vertex every 0.55 inches (with respect to the original paper maps). This prevents problems when the data is projected to another coordinate system.
Edgematching
The edgematching was carried out mannually to establish a "cartographically pleasing match across ONC boundaries" Priority was given to the best data being matched. Many areas are plagued by inconsistancies between modules. No edge matching was attempted in these areas. Generally, attribute information will indicate the source and extent of the edgematching problem where it exists.
Annotation
Two methods are used to annotate features in the database. Where the features are explicitly described in the database with a point, line, or polygon, the annotation is generally included as an attribute. For features that do not contain a specific an explicit representation (e.g., a mountain range) annotation files are included. Generally if an attribute existed describing the feature, then no annotation is supplied for it. If there is no attribute for the feature (the feature is not represented by a point, line, or polygon in the
database), or if the attribute for the feature does not give a complete description, then the complete description is represented in the annotation. The starting point of the annotation generally indicates the location of the feature.
The annotation was put together in Arc/Info version 5.1.1 using the fonts in
"plotter.txt".
Data Quality
Data quality is documented at three levels:
- Feature
There are attribute tables for many of the features (the
table names end in 'STAT') that give staus information for individual primitives
in the database.
- Layer
DQNET describes the data quality of individual layers for each map
sheet used in the compilation of the DCW database.
- Source
DQNET also describes the data quality of individual map sheets
used in the compilation of the DCW database. Attributes describe characteristics
of each sheet.
The horizontal accuracy is 1600 to 7300 ft (90% CI); the vertical accuracy
is 160 to 2100 ft. (90% CI).
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