One thing you cannot avoid once you start dabling in the world of GIS is the idea of a coordinate system. If you remember back to high school math, you will have done many excercises plotting out points and lines on a basic graph with a horizontal X axis and a vertical Y axis. This type of graph uses a Cartesian system, with the two axis meeting at a point usually called 0,0 - these two numbers are the coordinates representing X and Y respectively. As you know our world is not flat, truly, I kid you not. It would make life much easier for us geospatial folks if it was but sadly no. In order to talk about the same features on the earth in a consistent way, geographers and people who love math have figured out sets of mathematical equations to assign coordinate systems to our round(ish) globe.

Our page on Map Projections has more details on the nature of these systems.  There are two main types of coordinate systems- the cartesian system as mentioned above which uses X,Y values to define a location on a flat (projected) surface and geographic coordinates which refer directly to a location on the round globe which are called latitude (the horizontal X value) and longitude (the verical Y value).  For a geographic coordinate system these numbers look like 37.45415, 120.541254 if you are in the northern hemisphere and like -28.541364,40.654154 if you live below the equator. Most GIS programs will default to this type of numbering format. If you are unlucky you may get lumped with some data from a GPS unit or some other source that uses a far more confusing way to denote geographic coordinates- the other common way to record them is using Degrees, Minutes and Seconds. We're not talking about time here, it's far more complicated unfortunately. The oldest way to measure the distance around and along the globe is using these latitude/longitude values that have been split up into degrees as the major unit (similar to miles as an example) and then within those we have a smaller unit called Minutes (simialar to say feet as a measurement), then we have a finer measurement again called seconds which normally have a decimal place and a few more digits below that (kind of similar to inches now- much more precise). There are tools to automatically convert from the old Degrees, Minutees, Seconds format into what we see more often- Decimal Degrees. From 32⁰ 12' 18.43523" into 32.20512.

Calculations of distance, area and other measures are much more difficult with geographic coordinates as they reflect a curved surface, not a nice flat surface. For traditional cartesian coordinates it is very easy to calculate these things manually and they make more sense to the user- much easier to look at two X,Y coordinates measured in feet or meters and get some idea of their size or separation than to look at two latitude values in degree/minute/second format! If you use these DMS formats often as a geodisist or geospatial analyst you might make sense of them but it takes some time for them to become helpful.

Luckily your GIS program will deal with these at minimal strain to you. What you should be aware of is that when you open a new data file in a GIS program it may not know what system the data are from- you need to tell the software which system to use. This is where it helps to have some idea about coordinates and projections!