I agree it would be great to chose the location and I will try to come up with some solution.
Essentially, the main challenge here is that this is 99% statically hosted project. You download the full list of fuel stations and the app then shows you the closes ones.
We have around 7k fuel stations across the UK, which is 350kb compressed, so not a big issue.
However, full postcode list (1,768,727 postcodes) is 20MB compressed (62MB uncompressed), that won't be acceptable to be handled on the client device.
I am thinking of cutting off the last two characters off postcode, that will give us 11k rows and 286kb with around 1 mile precision in densely populated areas, that will do the trick.
In any case, I only started working on it on Sunday. Still have couple of ideas to implement, but need to do my day to day work :)