Building Windows Phone applications, you have options for data. Sometimes you might want to use XML files. Warning: using XML files is like serialized Isolated Storage data – you need to load the entire document into memory to filter it. But, what if your data is already XML? You might want to reuse your assets.
In this sample, I will build out a cascading set of pages letting the user pick Country > then Region > then City. It’s a real scenario, not in any way unique to XML-related data.
Read the whole article here.