A Quick Guide to Using Lat/Lon Coordinates

Plotting and Measuring Latitude

Latitude represents a north-south position on the earth. I use the rhyme “tropical latitudes improve my attitude” as a memory crutch. Latitude increases as you move towards the poles. Because the lines of latitude are parallel and evenly spaced, a degree of latitude represents a constant distance on the ground.

Place the ruler so that it spans the lines of latitude
that the point to be measured or plotted falls between.
Orient the ruler north to south.
The zero minute end of the ruler should be on the southern line of latitude.
(In the northern hemisphere.)
To measure the latitude of a point on the map:
- Read the value from the ruler at the point
- Add it to the latitude of the line at the zero end of the ruler.
To plot the location of given coordinates:
- make a small tic on the map to indicate the line of latitude the coordinates fall on.

Plotting and Measuring Longitude

Longitude represents an east-west position on the earth. Longitude increases as you move away from the prime meridian, or 0°, in Greenwich, England. Because the lines of longitude converge at the poles, a degree of longitude represents a varying distance on the ground, depending on the latitude.

Place the ruler so that it spans the lines of longitude that the point to be measured or plotted falls between. The ruler will need to be on a diagonal to fit.
To measure the longitude of a point on the map:
- Slide the ruler vertically, keeping the ends on the lines of longitude marked on the map, until the edge of the ruler touches the point to be measured.
- You may need to extend the lines of longitude above or below the map to properly position the ruler.
To plot a longitude coordinate:
- Make a small tic on the map to indicate the line of longitude.
- The point of interest is located where the plotted lines of latitude and longitude cross.

Want more details?

Latitude and Longitude Defined
Formats and Symbols
Plotting and Measuring Lat/Lon
Video Tutorial on Plotting and Measuring Lat/Lon
An Exercise to Test Your Knowledge
Answers to the Exercise
MapTools Lat/Lon Rulers Map Datums and why they are so important