The latitude and longitude is set by default from the timezone you chose in the system. Unless you continuously create plans for foreigners, I don't see the need for this request and anyway, if you want to be precise, each plan will have a different latitude and longitude that you'll have to change each time you start a new plan.
See this long list of time zones I wrote for the program? It gives the latitude and longitude of the biggest city in each known timezone (for example New York City for US/Eastern time zone). So, either you changed the timezone in your system for whatever reason, or retrieving the timezone you chose is buggy in your environment. Could you check again please?