Major latitudes and longitudes are shown as lines across the map or as tick marks in the margins. On most maps or charts, only selected latitudes and longitudes are completely labeled. To prevent clutter, other lines are labeled with partial numbers. For example, only the minutes of arc are shown. The standard way to describe a location with geographic coordinates is to state the latitude followed by the longitude. For example, 46°25'09"S, 105°57'15"E.
For a rough approximation of the latitude and longitude of a location on a map, look at the nearest latitude and longitude lines that surround the location. Visually estimate where the location is relative to the nearest latitude and longitude lines. Take into account that there are 60 minutes of arc in each degree and 60 seconds of arc in each minute of arc.
For more precise results, use a ruler to measure the distance between the location and the nearest lower latitude line, and then measure the distance between the nearest higher and lower latitude lines. Divide the first distance by the second distance to obtain the proportional distance. Convert the proportional distance into angle units and then add the result to the nearest lower latitude line. Calculate the longitude in a similar manner.
Example of how to determine geographic coordinates on a map
On the map below, the proportional distance between Location A and the nearest lower latitude line is 17 mm/38 mm = 0.45. The angular distance between the longitude lines on the map is 1' = 60". Converting from proportional distance to angular units gives 0.45 x 60" = 27". Adding this result to the nearest lower latitude
line gives 53°01'00"N + 27" = 53°01'27"N.
