Chapter 2 - Turning a Globe into a 2-d map

Visualize taking the globe and placing a grid system on it, aka geographic coordinates. Doing this is termed projection. Now take this projection, this grid system and convert it into another preexisting grid system so you can share your data with data from another person's work. This is called reprojection and are both the first and second steps towards making a GIS. 

Because of this I have to understand how to make a geographic coordinate system for the globe which I can then reproject into a 2-D map of an area for my GIS. 

First, longitude, latitude, meridians (think of Greenwich England), and parallels (like the equator). The prime meridian is a line that goes north to south. From this line angles can be drawn to the left (west) and to the right (east). These angles drawn away from the prime meridian are longitude lines. Th equator is a parallel and is called 0 degrees latitude. From this line angles are drawn north and south, these lines are called latitude lines. Consider the globe as if on a x-y plane. Longitude lines are x values and latitude lines are y values. 

Conception of the globe. The globe is not a perfect sphere. Image it as being wider around the equator than it is from the north pole to the south pole. This shape I am describing is an ellipsoid. The earth is actually a very weird shape. It is in the shape of a geoid. Imagine if every GPS around the world sent in their location, and the shape of the land mass of the world was mapped out, it would show this strange shape which we call geoid.

Using a geographic coordinate system of the globe has to match up with a global model that depicts the earth as a mathematical shape. Imagine now that you have a model orange peel with a coordinate system. To take this sphere and turn it into a flat map of the orange is going to be impossible. So what you do is you figure out where you need the map to be most accurate and you try to match that section up as best you can to form a map. This is map projection. Datum is a concept that I left out of the discussion. A datum refers back to the sphere model that we made. You can match up the sphere to the location on the globe you need to be most accurate. Doing so makes your datum best suited for you but maybe not for other people.

Map projection types. A conformal projection somehow preserves angles and shapes. An equivalent projection  represents areas of the globe in relative size. An equidistant projection maintains consistency of scale along certain local lines. An azimuthal projection maintains certainlocal directions. When you make a map projection you include the type of projection in the map name.