Vector Vs. Raster Quad Maps
TopoDepot and TopoDepotOnDVD generate Vector 7.5 minute quad maps. These are CAD/GIS
drawings where each road, stream, and contour line are individual entities. This
is completely different from Raster quad maps which are simply paper maps that have
been run through a scanner and geo-referenced (although we also provide the raster
quad maps and aerial/satellite photos).
The entities on our Vector maps are on many different layers, according to their
type. For example, major roads are on a different layer than minor roads or streams.
Additionally, contour lines are 3D polylines. This makes for a very easily manipulated
CAD or GIS drawing.
The difference between Vector maps and Raster maps is analogous to the difference
between a word processing document and a scanned document. The word processing document
is a whole lot easier to change, move words around, add new paragraphs, or run a
spelling checker than a scanned document. Likewise, it is much easier to modify,
move, add new entities, or analyze a vector CAD drawing than the corresponding scanned
map.
TopoDepot also provides access to the USGS Digital Elevation Models (DEM) that are
used within TopoDepot to generate the 3D contour lines. Several output formats,
including XYZ, NEZ, and AUF files allow your 3D Surface Analysis Program, such as
AutoDesk Civil 3D, to use this 3D surface DEM data. You can use this 3D surface
data to calculate drainages, viewsheds, cut/fill, create 3D images, and many other
engineering and planning tasks.
