U.S. Coast & Geodetic Survey/NOAA Steps to Creating a Nautical Chart Historic types of surveys required – Astronomical Observations – Land survey (triangulation) – Tide Gauges – Shoreline Mapping – Hydrography

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.

View through Telescope at desired star Star aligned with cross-hair

Astromical Observations performed at this site to determine initial latitude, longitude, and azimuth. Survey Network

TRIANGULATION 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 MEASURED BASELINE 1 Angle measured MEASURED BASELINE 2 = survey mark STEPS

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 =Tide gauge

4.Plane table moved to another location and procedure repeated 5.Points of intersection define position of distant objects 6.Shoreline is drawn through intersecting points; also range & bearing determine positions 1.Plane table is set-up over known point 2.Paper map correctly oriented 3.Distant objects sighted upon and lines drawn from present position toward distant objects

PLANE TABLE MAPPING

Depths (soundings) are measured continuously along dotted lines. Sextant angle fixes are taken at locations indicated by green bars

HYDROGRAPHY Two sextant angles at periodic points along the launch’s path determine position of the launch

= survey mark GEODETIC SURVEYSHORELINE SURVEYTIDAL SURVEY = tide gauge HYDROGRAPHIC FIELD SHEET