The SALT app needs to know where you physically are to show you the correct stories and also to ensure your profile is shown to other people (don't worry - your exact location isn't shown to other people). The default setting is for SALT to use GPS to automatically work out where you are and show you people near you.
If you'd rather fix your location to a set point, simply toggle this setting off, and move the pin on the map. Manually setting your location is a SALT Premium feature. If you don’t have a SALT Premium subscription you will have to enable your GPS location. All of this is found in the Location section in Settings.