The ability to identify a Twitter account's location is driven by the location field in the Twitter bio, which is a free-form text field.
Twitter users can choose to fill out that field any way they prefer. Some users are very specific, for example: "NY, NY, USA." Others are more general — "USA" — and yet others opt for things like "Everywhere" or "the Moon." And sometimes, it's left blank because Twitter does not make it a required field.
Consequently, when you apply a location filter in Symplur, the results will not reflect 100% of the conversation. We find that a location filter by country will capture about 65% of a given conversation on average.