Latitude and Longitude
To navigate the globe and pin-point your position in the world one uses a coordinate system. There exists several coordinate systems for mapping the globe, but the most common is WGS84 latitude and longitude coordinates.
Latitude is vertical direction (Y axis) indicating how many degrees north or south of equator. North is positive direction. The values goes from -90° (South pole) to 90° (North pole).
Longitute is the horizontal direction (X axis) indicating how many degrees east or west of Greenwich meridian. East is positive numbers. The values goes from -180° (west of Hawaii US) to 180° (east of New Zealand), both meeting at the vertical date line in the middle of the Pacific ocean.
If an orange is held like a globe with the stem point at the North pole, then the longitude degrees are like the vertical boat-shaped wedges of the orange. Latitude degrees are more like horizontal cuts made by an egg slicer. This means that the distance per degree longitude changes the further north or south from equator, but distance per degree latitude stays the same.
At equator with 360 degrees for a full circle and circumsphere of ca. 40000 km (radius ca. 6378 km), each degree is ca. 111 km.
When writing coordinates the order is normally latitude (Y) before longitude (X), note that this is opposite of the mathematical notation (X-Y) used by cartesian coordinate system. The positive direction of latitude and longitude is same as cartesian coordinate system. Sometimes direction west and south are not written as negative numbers but as positive numbers with an added W or S.
Decimal Degrees - DD
The simplest way to specify coordinates is with decimal degrees, abbreviated DD. With 2 decimal the last digit is a precision of about 1 km. With 5 decimals the last digit is a precision of about 1 m. Add 3 more decimals and precision would be at mm level.
As an example of precision the Little Mermaid in the harbor of København DK is at location;
Decimal Degrees: 55.692867°, 12.599287°
|56°||13°||0 (only degrees)||~ 111 km|
|55.69°||12.60°||2||~ 1 km|
|55.69287°||12.59928°||5||~ 1 m|
DD notation is the ISO 6709 recommended format.
Degrees Minutes Seconds - DMS
There is an alternative notation that uses 60 counting, so called sexagesimal numbers. The degrees are subdivided in 60 parts, which can then in turn be subdivided by 60 parts. That gives an accurary of ca. 31 m at equator. Further subdivision are however not by 60 but by decimals.
The system is known as degrees-minutes-seconds (DMS), as minutes and seconds use 60 counting. However these are coordinates and have nothing to do with time, so talking about time makes a confusion of units.
The 60 counting makes geographic calcucations more complicated and has less accuracy than decimal degrees when using same number of digits.
Using DMS notation the Little Mermaid is at location;
Degree Minutes Seconds: 55° 41' 34.32", 12° 35' 57.43"
|Latitude||Longitude||# Subdivision Digits||Accuracy|
|56°||13°||0 (only degrees)||~ 111 km|
|55° 41'||12° 36'||2 (with minutes)||~ 1.85 km|
|55° 41' 34"||12° 35' 57"||4 (with seconds)||~ 31 m|
|55° 41' 34.3"||12° 35' 57.4"||5 (with 1/10 seconds)||~ 3 m|
DMS has less accurary than DD notation for same number of digits. Using DMS with 4 subdivision digits is ~3 times less accurate than DD with 4 decimals.
Due to the unnecessary complexity of DMS notation and lower accurary it is recommended to use the simpler DD notation.
Convert DMS to DD coordinates
Latitude and Longitude of Location
Microsoft Bing Maps and Google Maps can both be used to find the coordinates of a location.
Latitude-longitude from Bing Maps
In Bing Maps go to the location and place mouse pointer at exact location. Context click and the latitude and longitude coordinates will be displayed as part of the context menu in DD format. See image.
Latitude-longitude from Google Maps
In Google Maps go to the location and place mouse pointer at exact location. Context click and select "What's here?". This will display the latitude and longitude coordinates in the search field in DD format. See image.
Link to Google Maps
To provide a link to Google satellite map with coordinates use the following format, replacing [LatitudeDD] and [LongitudeDD] with the coordinates.
The Gëlle Fra (Golden Lady) in Luxembourg LU is located at lat-lon 49.60929°, 6.12936°. So link would be:
Disable 45° View in Google Maps
When Google Map is zoomed in it will change to a 45 degree bird view where available. This is not useful when pin pointing precise locations. To keep vertical view hover cursor over Map menu in upper right corner. This will open an Earth menu. In the Earth menu untick the 45° option.
Introduction to ISO 6709 - standard representation of geographic point location by coordinates.
Tags: Latitude, Longitude, coordinates, WGS84
Page link: <http://foersom.org/HowTo/LatLon.html>