Question: Per Diem API - How do I know which primary destination to use for a zip code?

(Also asked here: [https://stackoverflow.com/questions/59721807/using-opengsa-per-diem-api-how-do-i-know-which-primary-destination-to-use-for](https://stackoverflow.com/questions/59721807/using-opengsa-per-diem-api-how-do-i-know-which-primary-destination-to-use-for))

I'm using the Per Diem API specifically endpoint #5 Meals and Incidental Expense (M&IE) Breakdown Rates by Year.

If send the following:
`https://api.gsa.gov/travel/perdiem/v2/rates/conus/mie/2020?api_key={MY_API_KEY}`

I get:

```
[{"total":55,"breakfast":13,"lunch":14,"dinner":23,"incidental":5,"FirstLastDay":41.25},
{"total":56,"breakfast":13,"lunch":15,"dinner":23,"incidental":5,"FirstLastDay":42},
{"total":61,"breakfast":14,"lunch":16,"dinner":26,"incidental":5,"FirstLastDay":45.75},
{"total":66,"breakfast":16,"lunch":17,"dinner":28,"incidental":5,"FirstLastDay":49.5},
{"total":71,"breakfast":17,"lunch":18,"dinner":31,"incidental":5,"FirstLastDay":53.25},
{"total":76,"breakfast":18,"lunch":19,"dinner":34,"incidental":5,"FirstLastDay":57}]
```

which seems to be the dollar amounts by area. How do I know what area to use for a given zip code (is that even possible)? There does not seem to be a way to look up what the primary destination identifier should be and I am sure the end user will not know this information. They would only know city & state OR zip code.

For example, I want to either only get the values for Pittsburgh, PA for 2020 OR know which of the above I would use for Pittsburgh, PA (versus Boston, MA)