Using OpenStreetMap data in an offline C# webforms application

Question

As part of a project, I have to develop a offline C# application that can calculate the distance and journey time between two points. I'm planning on using data from OpenStreetMap but I'm not too sure what the process would involve. I do not want to use OSM's API but rather develop my own backend, to ensure continuity in case someone else decides to pick up the project to improve it. I have several questions:

• Where do I download a full map of the United Kingdom from the website?
• How would I overlay the postcodes, addresses, places of interests onto the map?
• How would this information be read by the C# application (i.e. when the user enters point A or B, it should be pulled from a central database and automatically calculate the distance and journey time between both)
• I want the information to be stored on the client side, without the need for a server - is this possible?

Answer 1

Please ask only one question at a time.

Question 1: OSM offers various ways for downloading data. In your case you should download a country extract.

Question 2: For displaying a map either use raster tiles or vector tiles. But before that you should decide whether you want to render your own tiles (in which case you will need some kind of tile server) or use available tiles from the web (in which case you will need constant access to the web).

Question 3: Ideally your C# application will just query a local PostgreSQL/PostGIS database.

Question 4: Which information? Everything? That would require lots of resources on the client for storing and querying the data.