10 
e There are no universal conversion factors for relating tide, vegetation, 
contours, and cadastral boundaries. 
In many areas, available 1:24,000-scale topographic maps could be used as 
cartographic bases. The upper wetland boundary could be interpreted from current 
color infrared photographs according to the applicable regulations and compilec 
on the map. This procedure would serve as a practical inventory at minimum cost 
and would satisfy general zoning regulations. It would provide a zone boundary 
between marsh and upland with an NMAS horizontal accuracy of about 40 feet. 
However, the increasingly popular orthophoto cartographic products have proved 
invaluable for mapping swamps, marshes, and other regions of overwhelming detail 
usually lost in conventional map symbolization. Compared with line map portrayal, o eo 
the orthophoto of a coastal marsh provides more information on the many features 
associated with identifying the boundary between upland and marsh. ® Besides 
matching the accuracy of conventional maps, the orthophotos show the actual 
pattern of vegetation and woodland as well as the lone tree, all visible roads 
and trails, the intricate meanderings of waterways, and other detail useful for 
position determination. Information on current land use can be derived from 
tonal differences in the photograph. 
On the 1:24,000-scale line maps, the definitive marsh boundary is lost by 
symbolization and therefore cannot be measured in terms of the map accuracy 
statement. Thus it appears desirable to prepare orthophotos for all the coastal 
wetlands to provide the best medium on which to delineate the upper wetland 
boundary. 
The photoimage base can be prepared as an orthophotomap or as an orthophoto- 
quad. The orthophotomap entails selective cartographic treatment with various 
features enhanced by line drawing and color separation. Since it combines the 
features of a line map plus the photoimage, its production is time consuming and 
expensive. The orthophotoquad, on the other hand, entails minimal cartographic @ e 
treatment; a few selected names and a grid reference system are included. The 
monocolor photograph itself provides planimetric information. The orthophotoquad 
is substantially cheaper to produce and the most up to date of the alternatives 
for base maps. Complete orthophotoquad coverage of the coastal wetlands could be 
completed within a few years and would serve many purposes beyond the delineation 
of the upper wetland boundary. The USGS has recently prepared several experi- 
mental color image maps using two synchronized multispectral cartographic cameras 
in a single aircraft. One camera contains black-and-white panchromatic film and 
the other black-and-white infrared film. The two sets of photographs are processed 
into orthophotos at the correct scale. During printing the two images are in 
perfect register and through the use of various inks, several different color 
renditions are possible. 
Since some areas of the coastal zone may require scales larger than 1:24,000, 
the scale chosen for study at Sapelo Island was 1:10,000. Six 1:10,000 orthophoto- 
quads, measuring 2.5 minutes of latitude by 3.75 minutes of longitude, cover most 
of Sapelo Island and the marshes fronting the mainland. The 1:24,000 Doboy Sound, 
Georgia, 75-minute quadrangle covers the same area. By NMAS, the horizontal & 
accuracy of well-defined points on a 1:10,000-scale map should be 28 feet or Q 
better. The relative accuracy between two points on a single map should be 
about 15 feet.