The document explains geodetic datums, defining horizontal datum as the relationship between the physical Earth and coordinates like latitude and longitude, and vertical datum as the baseline for measuring elevations. It outlines various types of datums including NAD27, NAD83, WGS84, and NAVD88, highlighting their ellipsoid foundations and current usage. NAVD88 is established as the reference for elevation measurements in North America.

14. 1. Geodetic Datum
►Also known as horizontal datum
►Defines the relationship between the physical earth and horizontal
coordinates such as latitude and longitude
2. Vertical Datum
►The zero surface from which all elevations/heights are measured.
►Defines level surfaces.
Types of Datum

15. ►NAD27 (North American Datum of 1927) uses the Clarke (1866)
ellipsoid.
►NAD83 (North American Datum of 1983) uses the GRS80
ellipsoid.
►WGS84 (World Geodetic System of 1984) used GRS80. Presently
uses the EGM 96 (Earth Gravitational Model 1996).
►North American Vertical Datum of 1988 (NAVD88). NAVD88 is
now the reference vertical datum for elevation readings in North
America.
Types of Datum