Spatial data are meaningless without properly referencing them.
All the measurements in surveying sciences are relative to some sort of pre determined controlled points (values). In Engineering/construction surveying, we are setting out horizontal or vertical points with reference to control points established within the site . These control points should be established by using the government control points. Traversing methods or Static GPS techniques can be use for this task. Accuracy should be the main concern. Government control points are always connected to the national grid system.
Hydrography, Remote Sensing, Photogrammetry and GIS data are also relative to a particular reference system such as national grid system. National grid system of a country is based on a particular ellipsoid (WGS84, Everest, etc.) . Ellipsoid is a mathematical (imaginary) model best fitted to a particular place on the Earth. Therefore ellipsoid is again relative to a particular place on the Earth.
What if we need to do some surveying measurements in mars. We may do the measurements with reference to a particular star. But is the star is stable? Scientists believe universe is continuously expanding. The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two co moving points.
As you may have noticed every measurement in surveying is related and relative to each other. Measurements are meaningless if they are not measured reference to a particular frame of measurements. Therefore surveying is a good example for relativity.
“When a blind beetle crawls over the surface of a curved branch, it doesn't notice that the track it has covered is indeed curved. I was lucky enough to notice what the beetle didn't notice”
<<Einstein, in answer to his son Eduard's question why he is so famous, 1922>>
