5 
: NMAS for vertical accuracy require that not more than 10 percent of the 
elevations tested shall be in error more than one-half the contour interval, 
i.e., & 5-foot contour should be correct within 2.5 feet at least 90 percent 
of the time. In checking elevations taken from the map, the apparent vertical 
error may be decreased by assuming a horizontal displacement within the per- 
missible horizontal error for a map of that scale. On the 1:24,000-scale map, 
the vertical error may be offset 40 feet horizontally to adjust the elevation 
an amount determined by the slope. 
In addition, the maps show several types of political and land-grant 
boundaries, which may bear some legal relationship to water or tidal features. 
However, the map positions of these boundaries are not legal evidence of correct 
location and cannot substitute for a cadastral survey. 
Since the 1:24,000 maps are the primary cartographic reference for the 
coastal zone land areas, it is important to clarify some of their limitations, 
which also serve to suggest the special requirements for coastal wetland 
mapping. 
.€e The maps may not be up to date, especially in areas undergoing rapid 
development. Consequently, recent dredging, filling, spoil piles, 
levees, or natural changes, such as sand erosion and accretion and 
channel shifts, are often missing. 
e Most of the coastal maps are line maps. Orthophotomaps are available 
for only a few coastal areas; however, orthophotomap production is 
increasing. 
e There is no distinction between fresh, brackish, and saline marshes; 
all are shown by the same symbol (standard blue tuft pattern). Wooded 
swamps , mangrove swamps, and submerged marshes have separate symbols. 
However, only a generalized interpretation is possible. 
e The marsh symbols bear little or no relation to the vegetation species; 
the field criteria may be something like "too wet to walk, too shallow 
to row, covered with grass." While reasonably accurate and acceptable 
in the main, the criteria are unreliable at the marsh boundary; further- 
more, at publication the definitive outline is lost by nature of the 
marsh symbol. Since the maps do not show a well-defined wetland 
boundary (except, of course, where it coincides with a shoreline), 
the map accuracy standards cannot be applied in the area between 
wetlands and upland. 
e Cadastral boundaries of land ownership are not shown. The transfer of 
deed descriptions to any type of map is a difficult, time-consuming 
procedure and, except for public lands, is not a responsibility of 
Federal mapping agencies. Usually scales larger than 1:24,000 are 
required. In most cases of land ownership, the boundary must ulti- 
mately be traced on the ground by a surveyor.