There is a difference between the APP (mobile) Nokia Maps and the API (web) for Nokia Maps
The distinct difference is Offline APP is for Nokia Mobile/Tablet
Can Nokia Maps be used in offline mode to avoid data costs?
Maps can be used offline to avoid data charges, however the following will not be available in Offline Mode:
View Satellite maps
View Terrain maps
Search the latest address/POI database
Real-time Traffic and Safety updates
Share your status, photos and location to your Facebook profile (Maps 3.03 and later)
Get Weather forecasts
See local event info from WCities (Maps 3.03 and later)
Access Lonely Planet city guides (Maps 3.03 and later)
Access the Michelin restaurant guide (Maps 3.03 and later)
Synchronize your locations with Nokia Maps on the internet
You can switch between Online and Offline mode by going to the Maps Settings and:
Select Internet or General
Select Connection or Go Online at Start-up
Please Note: Switching between Online and Offline mode in Maps will not prevent data charges through the user of Positioning settings such as AGPS and WiFi/Network positioning. These will need to be turned off in the Positioning Settings on your phone. Please see your phone manual for more information.
From User Experience OFFLINE mode is only good if you have all the data pre-loaded on the mobile device for the area you are in/or interested in.
OpenStreetMap with your own tile render will allow you full offline support in a desktop environment: