A look at how we determine our position on earth - latitude & longitude or easting & northing? The make up of a reference system as a recipe.
Altitude, elevation, height - what do we really mean?
Sections for general answers, for engineers, for surveyors and what can go wrong.
Earth is a bizarre unique shape. To make mapping easier we start by making a shape based on sea level (the green shape in picture 2). Then we put an ellipse around it to smooth it out.
Two reference systems are shown in picture 1 to the right. These are what we use to calculate positions on our earth.
The red dots are the centre of each ellipsoid, the origin of the shape. Each ellipsoid with its red origin, it's shape and it's orientation is called a DATUM!
You can see how the coordinates of a place change when you move from one datum to another. The green dots have the same lat/long. but are on different Datums.
Where am I?
Picture 1: Two places on earth,
with the same latitude/longitude
Picture 2: The geoid as an aprox mean sea level with ellipsoid of latitude/longitude lines
Did you know?
The Latitude & Longitude of a position on earth is NOT unique. Other places will have the same label
Latitude & Longitude is over a curved surface - Easting & Northing are on a flat surface
Land moves so coordinates change
There are many ways to describe an altitude - how do you know which one you mean?
Maps distort land - it's not necessarily what it looks like.
Do you really understand what your GPS/GNSS device is telling you?