### Coordinate Systems

### Overview

A fundamental element in representing spatial data is the coordinate system within which they are described. Coordinates, in our context, are sets of numbers used to specify the location of a points on the surface of the earth. There are several coordinate systems in use and in each case, the manner in which these coordinates are used is logical, consistent and universally agreed to by its users. This topic looks at the basic elements of all coordinate systems and examines the characteristics of the geographic coordinate system.

### Learning Outcomes

Upon successful completion of this topic you would be able to:

- Explain the components and functions of coordinate systems
- Explain the features of the geographic coordinate system

**Coordinate Systems**

In order to be useful, a coordinate system should have three main characteristics as follows:

- A known unit of distance measurement (e.g. feet, metres, degrees)
- A clearly stated origin (generally located in a convenient location)
- A clear statement of the orientation of the axes at the origin

The above characteristics generally assume that the system also meets the following criteria:

- It has two sets of lines that are distinct from one another (axes)
- Every line from one set intersects every line from the other set, only at one point
- No two lines from the same set intersect each other

**Activity 1 – Research Coordinate Systems**

Use an internet search engine to find internet sites that provide clear useful information, and make notes on the following:

- Cartesian Coordinate System
- Grid North
- True North
- Polar Coordinates

**Geographic Coordinate System (GCS)
**

The most accurate means of locating a point on the surface of the earth (represented as a spheroid) is through the GCS ie. using coordinates in the form of Degrees of Latitude and Degrees of Longitude. The earth is fully described by a network of lines of Latitude and lines of Longitude, called a **Graticule**.

**Activity 2 – Description of the GCS**

The ESRI help page provides a very useful description of the GCS. Please read and make notes from the following link:

**Activity 3 – Further information on the GCS**

Perform a search on the internet for further information regarding the GCS. In your search, make notes on the following:

- Spheroid
- GRS 1980

**Activity 4 – Post your Summary**

Write a brief post in your blog, no more than four paragraphs, designed to teach a non-technical person the basics about coordinate systems and the GCS. You should include links to any site you have found to be useful. Name this post “Coordinate Systems – the basics”.

**Activity 5 – Comment on postings**

Post a comment on the summaries posted by at least two classmates.