Topographic mapping.
Ellipsoid taken to be 800ft above the NAD27 reference ellipsoid.
Definition: JSON
{ "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json", "type": "GeodeticReferenceFrame", "name": "NAD27 Michigan", "ellipsoid": { "name": "Clarke 1866 Michigan", "semi_major_axis": { "value": 20926631.531, "unit": { "type": "LinearUnit", "name": "US survey foot", "conversion_factor": 0.304800609601219 } }, "semi_minor_axis": { "value": 20855688.674, "unit": { "type": "LinearUnit", "name": "US survey foot", "conversion_factor": 0.304800609601219 } } }, "scope": "Topographic mapping.", "area": "United States (USA) - Michigan.", "bbox": { "south_latitude": 41.69, "west_longitude": -90.42, "north_latitude": 48.32, "east_longitude": -82.13 }, "id": { "authority": "EPSG", "code": 6268 } }