There are a number of base maps available for you to use. Some are completely free, others are freemium and some only available if you are in a standard or professional subscription.
By default any new map will use OpenStreetMap which is free. You can then select a different one by expanding the list.
| Base Map | Free | Freemium | Free in a Standard or Professional subscription | 
| OpenStreetMap | x | 
 | 
 | 
| Ordnance Survey | 
 | x | 
 | 
| Ordnance Survey Light | 
 | x | 
 | 
| Ordnance Survey Leisure | 
 | x | 
 | 
| Ordnance Survey c.1900 | 
 | 
 | x | 
| Stadia Maps Imagery | x | 
 | 
 | 
| Stadia Maps Imagery with labels | x | 
 | 
 | 
| Aerial Imagery (25cm/px) | 
 | 
 | x | 
| Blank | x | 
 | 
 | 
| Environment Agency Lidar | 
 | 
 | x | 
Freemium base maps are free to view at certain zoom levels, you will need to purchase Ordnance Survey Credits to view more detailed data. This guidance shows how.

