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WHERE FREQUENT REFERENCE MUST BE MADE TO LANDMARKS, TO 
LIGHTS AND BUOYS, AND TO FEATURES OF THE NEARBY LAND. 
We hold that a nautical chart is an instrument of navi- 
gation that must be kept up to date to serve its intended 
purpose, l.e., to insure the safety of navigation. The 
larger part of our charting effort is devoted to maintenance, 
particularly the maintenance of the considerable number of 
large scale charts. For example, in 1959 we published only 
20 new and reconstructed charts but we revised and reprinted 
= charts, or nearly 65% of the total number of charts on 
ssue. 
It is against this background of large scale charts 
with their requirement for frequent revision that our pho- 
togrammetric procedures have been developed over the last 
30-odd years. We use nine-lens and single-lens photography 
together with limited ground surveys and stereoscopic plot- 
ting instruments: 
1l. TO PERFORM AEROTRIANGULATION, to position land- 
marks and aids to navigation, to provide alongshore 
control points for inshore hydrography, and to po- 
sition individual models for map compilation. 
2. TO PREPARE DETAILED LARGE SCALE MAPS showing 
the shoreline, alongshore rocks and structures, 
indications of shoals and channels visible in the 
photographs, and the land features adjacent to the 
shore. These are prepared ahead of hydrography 
for the guidance of the hydrographer and are used 
together with the hydrographic survey for the con- 
Struction or revision of the chart. 
3. TO CORRECT THE AIDS, LANDMARKS AND LAND FEATURES 
ON CHART DRAWINGS directly from new aerial photog- 
raphy to bring this information up to date just prior 
to reprinting and reissue of the chart. 
We took our first experimental color photography just 
two years ago in reference to an unusual shoreline mapping 
problem--we were amazed and delighted with its ability to 
RECORD, AND TO SEPARATE DETAILS NOT SEEN ON PANCHROMATIC 
FILM. The amount of field work required in our photogram- 
metric mapping is generally in inverse ratio to the clarity 
with which certain features such as landmarks, lights and 
beacons, rocks awash, and inlylng shoals and channels can 
be seen and identified with certainty on aerial photographs.