U.S. Coast

1
U.S. Coast Geodetic Survey/NOAASteps to
Creating a Nautical Chart

• Historic types of surveys required
• Astronomical Observations
• Land survey (triangulation)
• Tide Gauges
• Shoreline Mapping
• Hydrography

2
Theodolite instrument for precise astronomical
observations to determine latitude, longitude,
and azimuth
Astronomical observations were necessary to
determine the position and orientation of
selected points in a survey network.
3
View through Telescope at desired star
Star aligned with cross-hair
4
Survey Network
Astromical Observations performed at this site to
determine initial latitude, longitude, and
azimuth.
5
TRIANGULATION
Angle measured
Angle measured
survey mark
MEASURED BASELINE 1
Angle measured
Angle measured
MEASURED BASELINE 2
STEPS

• Baselines (BL) 1 2 are measured
• All angles of the triangles are measured
• Sides of all triangles are computed
• Computed length BL2 is compared to measured
  length of BL2

6
TIDE GAUGES

• Tide zone boundaries shown in red and orange
• Within each zone tidal height and time
  correctors are equal
• Tidal data required to correct depths and to
  determine horizontal position of shoreline

7

• Plane table is set-up over known point
• Paper map correctly oriented
• Distant objects sighted upon and lines drawn from
  present position toward distant objects

1. Plane table moved to another location and
   procedure repeated
2. Points of intersection define position of distant
   objects
3. Shoreline is drawn through intersecting points
   also range bearing determine positions

8
PLANE TABLE MAPPING
9
Depths (soundings) are measured continuously
along dotted lines. Sextant angle fixes are taken
at locations indicated by green bars.
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7.2
9.1
9.5
5.1
7
7.9
9.3
9.4
6.1
8
5.7
8.5
7
6.5
8.9
7.8
5
8
9
7
5.2
9.2
6
9.2
5.5
7.1
9.5
8
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HYDROGRAPHY

• Two sextant angles at periodic points along the
  launchs path determine position of the launch

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GEODETIC SURVEY
SHORELINE SURVEY
TIDAL SURVEY
HYDROGRAPHIC FIELD SHEET
FINISHED NAUTICAL CHART