# Coordinate reference system

There are three ways of defining the used coordinate reference system:

1. EPSG -code
2. PROJ.4 -string
3. WKT version 1 -string

EPSG -code is a numberic value, which defines the coordinate reference system. If unsure which EPSG code is being used for the project, EPSG.io -web page is a great source to search for systems. 

<figure><img src="https://1605669813-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FqIBa9qorv0XHooVd4ozT%2Fuploads%2FF7mVVuj3KcYvhatKkDor%2FCRS_EPSG.png?alt=media&#x26;token=344cafae-762b-4bce-83b1-2050de9e089f" alt=""><figcaption><p>Project configuration - Defining CRS with EPSG -code</p></figcaption></figure>

PROJ.4 and WKT allow custom localization for the coordinate systems, because it enables changes to the towgs84 -transformation values. PROJ.4 and WKT -strings are widely used by other similar systems. These can also be fetched from external web pages.&#x20;

Area of use restricts the map and this allows the map interface to work faster.&#x20;

<figure><img src="https://1605669813-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FqIBa9qorv0XHooVd4ozT%2Fuploads%2FxxU2twleQeOKTYOzeXMY%2FCRS_Custom.png?alt=media&#x26;token=e785a745-ceff-4e2e-9a53-5e4ae002acc6" alt=""><figcaption><p>Project configuration - Defining CRS with Custom definition</p></figcaption></figure>