Chart accuracy is hard to determine exactly. Several things need to be
taken into consideration.
The first and most important factor to consider
is that a chart can be only as accurate as the survey on which it is based.
To judge the accuracy and completeness of the survey, take note of its
source and date. Usually, early survey dates indicate that the chart may
have several irregularities.
A chart must be tested before it may be used
with a high degree of confidence.
In heavily trafficked waters, a chart is
normally quite accurate due to more thorough survey.
Tip: Another clue with which to determine accuracy is the abundance
or absence of soundings.
Infrequent soundings are an excellent indicator
that the survey was not of great detail.
Compromise is sometimes necessary in chart production, as scale,
clutter, and other factors may preclude the presentation of all
information collected for a given area. The National Ocean Service
publishes about 1,000 charts covering in excess of 86,000 miles of
shorelines. DMAHTC publishes an even greater amount.
Charts are an aid to navigation and must be used with a certain amount
of caution as they are not a complete guarantee of safety. Every QM
team is responsible to report any changes or errors they may encounter
on the charts they use.
In the back of each Notice to Mariners is a form
that may be filled out listing any discrepancies on charts. A radio
message may also be sent to DMAHTC Attn: NTM.