# Selecting the Coordinate Reference System

The **Coordinate Reference System (CRS) **enables the Earthâ€™s surface to be mathematically transformed and rendered on screen. The CRS is the reference used to interpret and report spatial positions in datasets.

## Notes on Coordinate Reference Systems

- A SIS Workspace Definition (SWD) has a default coordinate system (or more precisely both a
**Coordinate Reference System**and a**Viewing Projection**). - Each SWD has a
**Coordinate Reference System**that it remembers. - Each map window can have a different
**Coordinate Reference System**. This means you can have the same SWD displayed in different windows with a different**CRS**in each window. - When you start a Cadcorp SIS Desktop session, the default
**Coordinate Reference System**is Latitude/Longitude.OGC.WGS_84 (this is editable). New SWDs adopt this**CRS**automatically. - When opening an SWD, it uses the
**Coordinate Reference System**active at last Save. This can be changed anytime. - Each map window can use a different
**Coordinate Reference System**. You can select either a**Viewing Projection**or a**CRS**for the current window using CRS.

The **Viewing Projection** is used to present graphics on screen. If you choose a **Viewing Projection**, Cadcorp SIS Desktop makes the **Coordinate Reference System** compatible with it.

If you choose a **Coordinate Reference System**, the **Viewing Projection** is made compatible.

Alternatively you can change the **Coordinate Reference System** by clicking on the globe icon located on the right hand side of the status bar:

The following example shows some Ordnance Survey Meridian data. First it is displayed using its standard **Viewing Projection** (OSGB 1936.British National Grid), then using a Latitude/Longitude **Coordinate Reference System**: