Longitude & Latitude

April 30, 2007 - 6:49pm — mkabot

Longitude and Latitude combined make up coordinates that can be used to locate an object anywhere on the earth.  There are different representations for these numbers.  This section will describe the different formats, how to convert between them, and which ones you should be using.

WGS-84 is the "datum" definition that is standard to all current GPS units.  It was developed globally in 1984.  The North American standard NAD83 is for all intensive purposes an equivalent.  For the most part you should not have to worry about what "datum" type a set of coordinates are in.  It is helpful to understand that there is more than one though.

On the other hand, you will most likely need to deal with coordinate "formats".  These are the most common formats.

  • Degrees  & Minutes (MinDec)
    • This is the format you will want to use for all GPS applications
    • It breaks a coordinate down into two numbers: (1) degrees; (2) minutes.
    • Minutes include a decimal representation for seconds
    • Example:   N 43° 08.156  W 077°  26.652
    • See how there are two numbers (one with a decimal place) for each coordinate?
  • Decimal Degrees (DegDec)
    • This format uses a single number which includes minutes and seconds as a decimal part of degrees.
    • Example:  43.135933  -77.4442
    • See how there is only a single number for each coordiante?
  • Degrees, Minutes, Seconds (DMS)
    • This format represents each component of a coordiante (degrees, minutes, seconds) as a separate number
    • Example: N 43 08 09  W 77 26 39
    • See how there are three numbers for each coordinate?
  • Universal Transverse Mercator (UTM)
    • The previous three formats all used the same reference model for describing a location, only varying by the format in which the location is written.
    • UTM is a completely different reference model for location.
    • You will probably never have to use it, but you will see it and it helps to understand what it is.
    • Example: 18T E 301213  N 477810

Many GPS units have tools to convert between the above formats.  Here are a few online resources for datum/format conversions.

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