Imagine standing at the exact center of the Earth and shining a flashlight outward in any direction. Where that beam of light hits the surface of the Earth is a point. To describe which direction you aimed the flashlight, you use two angles: how far north or south of the equator (latitude), and how far east or west of a line through Greenwich, England (longitude). Those two angles together give every point on Earth a unique, permanent mathematical address — its Geodetic Ray coordinate.

A property boundary in this system is simply a list of those ray addresses, entered in order around the perimeter of the parcel. Instead of saying "start at a bent piece of rebar in the ground and go 660 feet north," you say "start at ray 38°42'39.152" N, 121°03'47.299" W and proceed to ray 38°42'39.152" N, 121°03'10.891" W." The distance between those two rays — computed mathematically to better than one millimeter — is the legal boundary. No rebar required.

An important thing to understand about longitude lines: The lines of longitude (the north-south lines on a globe) all meet at the North and South poles, like the segments of an orange. This means that the distance between two longitude lines gets smaller as you travel toward the poles. At the equator, one degree of longitude is about 365,000 feet. At 38°N — Sacramento's latitude — it is about 288,000 feet. At the North Pole it is zero. This tool accounts for this automatically in every distance calculation. Lines of latitude (the east-west lines) behave differently — their spacing stays nearly constant at about 364,000 feet per degree everywhere on Earth.

Altitude also affects the distance between ray intersection points: Two rays that are the same angular distance apart will intersect the Earth's surface farther apart at higher elevation than at lower elevation — because a higher surface is physically farther from Earth's center. A monument on a mountain at 8,000 feet and one in a valley at 200 feet, even if aimed at the same two angles, will produce slightly different surface distances than if both were at sea level. This tool computes three distance values for every pair of points: the pure ellipsoid arc (as if everything were at sea level), the chord (the straight-line distance through the Earth), and the ground arc (which accounts for the actual elevation of the two points). The ground arc is the most useful for comparing to what a total station would measure in the field.

Tectonic plate motion: The Earth's crust moves slowly — California drifts northwest at roughly two inches per year. This is already tracked by the National Geodetic Survey (NGS) using thousands of continuously operating GPS stations. GRS handles this the same way geodesists already do — by stating a date (called an epoch) with the coordinates. "Epoch 2010.0" means these are the coordinates as of January 1, 2010. Future surveyors apply a known, computed correction for plate motion. The fence stays. The legal description updates on a schedule — not in a courtroom.

Subdivisions use the existing degree/minute/second system you already know. One arc-second of latitude is about 101 feet. One arc-second of longitude at 38°N is about 80 feet. To match the precision of RTK GNSS equipment (±0.1 foot), coordinates need to be expressed to three decimal places of arc-seconds (0.001") — well within what modern equipment provides routinely. Parcels can be subdivided by halving the angular separation between any two rays: 1° → 30' → 15' → 7'30" → 3'45" → 1'52.5" → and so on, as many times as needed.

Proposal paper in preparation. For information, to submit measured monument coordinates, or to support this effort, use the feedback form. Every field measurement entered here is a contribution to a shared resource that benefits every surveyor who works in the same area.