I always remembered the difference between Longitude and Lattitude by the way the word "Lattitude" is similar to the word "Ladder".

Original Message:

Sent: 06-13-2019 03:35

From: Peter Horsbøll Møller

Subject: Confused by coordinate systems?

Thanks, Susan.

Even though I have worked in the GIS & LI space for more than two decades, I have always struggled to remember the difference between Longitude and Latitude, eg. which refers to the X axis and which refers to the Y axis.

I think this quote of yours just gave me a clue to how to remember:

"*The Longitude values range between -180 to +180°. Latitude values range between +90° to - 90°.*"

The **Longitude**, the X axis, has a "**longer**" range. I'll try to use this next time.

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Peter Horsbøll Møller

Pitney Bowes

Original Message:

Sent: 06-11-2019 08:58

From: Susan Bardet

Subject: Confused by coordinate systems?

What is the difference between latitude/longitude and Easting/Northing?

Latitude/longitude, Easting/Northing, X/Y are ways we uniquely identify a position on Earth and are also called coordinates. There are 2 coordinate systems namely geographic and projected.

A geographic coordinate system uses a spherical surface and a position is identified by its latitude and longitude. Latitude and Longitude are angular units of measure and are denoted in degrees minutes and seconds or decimal degrees. The Longitude values range between -180 to +180°. Latitude values range between +90° to - 90°.

When we create a map we project a sphere (Earth) onto a flat surface and we use projected coordinate systems to do this. The latitude and longitude are converted to X and Y coordinates. During this transformation the surface of the earth is distorted. There is no perfect map projection and one chooses a projection based on what distortion is acceptable for their purposes. Projections is a complex topic which I do not intend to touch upon in this article. After transformation Latitude is denoted by Y (northing) and Longitude by X (Easting). The most common units of measure in projected coordinate systems are meters and feet. For example UTM is a common projection, a location is identified with easting and northing and the units are in meters.

Summarizing the above, the units for Latitude and longitude is degrees, minutes and seconds and the units for Easting and Northing is linear the most common being meters and feet. You can find several free convertors online to do the conversions for you or you can attempt it yourself in excel. Below are a 2 websites where you can convert

https://www.bgs.ac.uk/data/webservices/convertForm.cfm

https://gridreferencefinder.com/

I have drawn a map below to illustrate the above explanation. The black grid lines are Latitude and Longitude and in red are the Eastings and Northings.

The position of Pitney Bowes office in Henley is

Latitude 51.553299 Longitude -0.92593001

X(Easting) 474565 Y (Northing) 184370

Grid reference: SU 74565 84370

If you have a large number of coordinates to convert then this is best done within a GIS software. How this is achieved would be the topic of another article.

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Susan Bardet

Software Support Engineer

susan.bardet@pb.com

Pitney Bowes

Henley-on-Thames

RG9 6AB Oxfordshire

pitneybowes.com

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