Google Maps Coordinate Format

[+Team Engage]

Pre-summary: The correct format is Sxx yy.zzz, Eaaa bb.ccc

 

I have had some recent trouble inputting coordinates into Google Maps. The most recent issue was trying to find the location of a mystery cache with coordinates -33.12644, 138.35911.

 

Inputting that data into Google Maps gave me a location about 25km west-north-west of where I expected the cache to be. I contacted the owner, and he sent me coordinates in the format s33 12.644, e138 35.911. As you can see, the numbers are exactly the same, however this led me right to where I expected the cache to be.

 

The reason for the difference are that Google Maps recognises several different formats for GPS coordinates.

 

Almost all GPS devices (and Geocaching.com's maps) use the format known as WGS84. This is a coordinate expressed in relation to an arbitrary point in degrees plus minutes. Thus you are using a system with, basically, 90 units (from the equator to the poles).

 

The other format is expressed in decimal degrees. A conversion is expressed below.

 

51.377318 (decimal degrees) = 51 + 0.377318

0.377318 * 60 = ~22.639

therefore, 51.377318° = 51° 22.639' (espressed as decimal degrees and then degrees plus minutes).

 

If you input the same numbers in the different formats, Google Maps assumes that you are using the correct system for the format you used. Thus Inputting the degrees plus minutes numbers (IE s51 22.639 IE 51 degrees, 22.639 seconds) as a single number (IE 51.22639) tells Google that you want to go to 51.22639 degrees.

 

So, in short, make sure that you always enter your coordinates as sxx yy.zzz, or if you HAVE to use xx.xxxxxx, make sure you convert the number first.

 

For interests' sake, here is a table of how much variance there is between towns at different locations around the world. Taken from Wikipedia (don't shoot me!) at http://en.wikipedia.org/wiki/Geographic_coordinate_system.

 

Longitudinal length equivalents at selected latitudes

 

Latitude Town Degree Minute Second ±0.0001°

60° Saint Petersburg 55.65 km 0.927 km 15.42 m 5.56 m

51° 28' 38" N Greenwich 69.29 km 1.155 km 19.24 m 6.93 m

45° Bordeaux 78.7 km 1.31 km 21.86 m 7.87 m

30° New Orleans 96.39 km 1.61 km 26.77 m 9.63 m

0° Quito 111.3 km 1.855 km 30.92 m 11.13 m

[+Team Engage]

Quick correction: it is all WSG84 format, it is just the difference in expressing it as decimal degrees and degrees plus minutes.

[+Viajero Perdido]

-33.12644 is not the same as W33 12.644. In the former, 12644 is a fraction of 100000. In the latter, 12.644 is a fraction of 60.

 

For a more clear example, -33.50000 is the same as W33 30.000.

 

Hopefully the coordinates you posted were changed for anonymity.

[+Chrysalides]

A few things:

 

1. As noted, if that is the final coordinates for a puzzle, you should edit it out of your original post.

 

2. You're confusing coordinate system, coordinates format, and datum.

 

3. You can enter coordinates into Google map in the format S 33 12.345 E 138 12.345

 

South and West is normally taken as negative, so you can specify it as -33 12.345 138 12.345, but I like to include the cardinal directions just so there's no confusion.

 

What you're describing is different ways of expressing the same coordinate system (latitude and longitude). A different coordinate system would be, say, UTM. Or ECEF. The datum is how the earth is modeled - WGS84 is one of the newest and the one in popular use right now. Since I'm not an expert in this field, this is what I've absorbed from my own reading, and if I'm mistaken please correct me.

 

Edit to add : you have an extra dot at the end of your URL - it'll link to a non-existent page. Can you remove the dot?

Edited March 18, 2011 by Chrysalides

[Suscrofa]

How things would be simpler if the only standard in use was simply decimal degree (standard in fact in the way data are stored or transmitted electronically) and UTM (and metric for all the rest too of course)!