Comment by socalgal2
My experience is that until you get the concentrated areas you don't get the actual diversity of the foods. When you have large areas of the same culture you start to get regional restaurants from the culture, specialty restaurants from the calture, because the market is big enough and business needs to distinguish themselves. You also get the ingredients as there's a big enough market to import them. When you don't have the concentration you just get the generic representation of the food from that country.
LA is much less dense than London so maybe you need concentration for those things, but we don't. We don't really have monocultural ghettoes. The beauty of London is how dense and intermixed it is. Cheek by jowl, as Shakespeare wrote.