001412L 1 0600049   22040000210000012921DQCG42500000;&1107DQCG.DDF0100;&DDF RECORD IDENTIFER1600;&CompletenessMODN!RCID!COMT(A,I,A)00081 D 1   00039   21040001080DQCG3480000001DQCG1VOID AREAS: No void areas.00793 D 1   00041   310400010080DQCG74480000002DQCG2The 7.5-minute series DEMS are based on a UTM grid. Hence, the scans
do not always have the same number of elevation posts due to the
variable angle between true north and grid north of the UTM coordinate
system. Any elevation post that falls outside of the 7.5-minute
quadrangle edge is dropped, i.e. there is no overedge. The 7.5-minute
DEM will be encoded as a non-ragged grid by filling with a background
post value to the edges of the minimum bounding rectangle.  The fill
value is distinguishable from all other elevation post values, and it
will be same value for all USGS DEM series encoded in SDTS. The Void
post value(-32767) will not be reused as the fill value, so the
original extent of the DEM data can easily be detected.00471 D 1   00041   310400010080DQCG42280000003DQCG3Void areas occur in the DEM as a result of interruptions
to the contours of the source graphic or DLG (eg. photoimages
overprinted onto a topographic map). Each DEM elevation post located
within a void area is assigned a false negative value of -32,767. The
percentage of void elevation values in the DEM, if present, was
calculated from the total number of grid posts in the DEM assigned the
false negative value.01225 D 1   00043   4104000100080DQCG117480000004DQCG4HYDROGRAPHY INCLUDED: For DEM Level 1 and 2, water bodies
contained in DEM data are edited when they conform to the following
criteria: 1) Type is a pond, lake, reservoir, or double-line drainage;
and, 2) Size of a pond, lake or reservoir exceeds approximately 1/2
inch at map scale (1000 feet at 1:24,000 scale, 4167 feet at 1:100,000
scale) along the major axis; or, 3) Size of a double-line drain
exceeds 1/4 inch (500 feet at 1:24,000 scale, 2087 feet at 1:100,000
scale) in width. For level 3 DEM's, the grid is constrained by all
major hydrographic features contained within a DLG hydrography
category, including drainage, lakes, swamps, and
shorelines. Elevations of hydrographic features are determined through
interpolation of contours using a registered DLG hypsography file. DEM
surfaces constrained to drains are treated as a special case of
hypsographic faulting where the DEM surface is simply creased along
the track line of the drain. Additionally, all grid cells are tilted
consistent with the direction of stream flow, along the track line of
the drain. There must not be any unsupported breaks or discontinuities
in the rate of slope of the drain.