Chapter 3 - Datums, Coordinate Systems & Units of Measure

A datum can be considered as a reference surface upon which the survey is based. For all project control and mapping performed for MDOT the following positioning parameters will be used unless otherwise directed by the MDOT Survey Consultant Project Manager or the MDOT Region Surveyor.

The Horizontal Datum that will be used for all projects performed for MDOT will be The North American Datum of 1983, 2011 Adjustment (NAD 83)

The Vertical Datum that will be used for all projects performed for MDOT will be The North American Vertical Datum of 1988, (NAVD 88)
Always use the most current Geoid Model available. NGS GEOID Home Page
New projects must use the current geoid model
- Exceptions for legacy projects requiring use of an older geoid model must be approved/discussed with the MDOT Consultant Project Manager or the MDOT Region Surveyor

3.2 Coordinate Systems

All MDOT projects will be based on the Michigan Coordinate System which is a Lambert Conformal Map Projection. More information regarding this coordinate system can be found in Act 9 of 1964, as amended.
- The appropriate Zone will be used depending on the project location, (North, Central, or South Zone)
- Combined Scale Factor from grid to ground as appropriate for the project and should be reported out to at least 12 digits right of the decimal.
  - All digits should be used in the averaging computation
  - Ground distance = Grid distance / Average combined scale factor

If ground coordinates are required, the Consultant Surveyor should contact the MDOT Survey Consultant Project Manager or MDOT Region Surveyor for the specific reporting format and conversion process from State Plane Grid Coordinates.

For projects over 5 miles in length with a North-South orientation contact the MDOT Survey Consultant Project Manager or MDOT Region Surveyor to discuss scale factor issues.

The following units of measure are to be used unless specified IN WRITING by the MDOT Survey Consultant Project Manager or MDOT Region Surveyor.

Distance measure:

All project data will be provided in International Feet. If a conversion from Meters to Feet is required, use the following conversion factor: 0.3048 Meters = 1 foot
Provide distance to the nearest hundredth (i.e. 0.01') of a foot.

Angular measure:

All angles must be formatted in Degrees, Minutes and Seconds to the nearest one second (i.e. 01°01'01").

Direction:

Area:

All area measurements must be reported in square feet to the nearest foot (i.e. 53ft²), or in acres to the nearest thousandth of an acre (i.e. 8.001 Acres).

Volume:

All volume measurements must be reported to the nearest cubic yard unless otherwise stated (i.e. 118yd³).

Horizontal Coordinates:

Provide all horizontal coordinates in northing and easting to the nearest thousandth (i.e. 0.001') of a foot.

Elevation/Orthometric Height:

Frequently Asked Questions