NOAA nautical cartographers receive information to be portrayed on nautical charts from a variety of sources. All NOAA paper charts are compiled at specific scales. Large-scale charts encompass relatively small areas and show a great amount of detail. Small-scale charts cover a large area, but show less detail.
Very often, source information—the raw material of nautical charting information—arrives at NOAA with a great amount of detail. For example, some U.S. Army Corps of Engineers survey blueprints show detail at a scale of 1:1,000. However, the largest scale NOAA chart encompassing the survey area might only be 1:20,000. It is impossible to show all the USACE survey data on the NOAA chart. Therefore, NOAA cartographers must generalize the data and only portray the important information represented by the USACE survey.
The example below illustrates a detailed survey that must be generalized on the nautical chart.