Why do we ask for your location?
In ControliQ, we ask for each user's location so we can work out the appropriate timezone for their work. Timezones are complicated - some countries observe daylight savings time, and others don't. Some countries do, but certain parts of the country might not.
We need to know your location accurately enough that we can work out what time it is for you now, or what time it was for you at a specific point in time. For example as I'm writing this at the end of November, a user in Johannesburg is two hours ahead of GMT (aka UTC), which puts them two hours ahead of London, 7 hours ahead of New York, 9 hours ahead of Phoenix, Arizona and 10 hours ahead of Los Angeles, California.
If we are looking at historic work though, we might be looking at some work that was done back in June - when that same person in Johannesburg was only one hour ahead of London, 6 ahead of New York, 9 ahead of Los Angeles and 9 ahead of Phoenix.
Those hours make meaningful differences - they can be enough to shift work from day to day, week to week or month to month depending on whether it's 11:30pm on a Monday night or half past midnight on Tuesday morning.
We don't use the location for anything else - other than working out the time where you are. Incidentally, asking someone to tell us their timezone alone doesn't help us work out the daylight savings bit, because someone in Phoenix would have (correctly) picked Mountain time but that doesn't help us work out that in summer their clocks don't go forward. To work out what time it is (or was) you need the location as well as the current date & time.
How come my home city/state/region isn't listed?
We use a standard list of locations (Official IANA TZ homepage or Wikipedia page on TZ database) which is specifically designed to identify the timezone - it isn't meant to be a complete list of places, and the only impact of the list is to work out how much of an offset from UTC your location has, whether it observes daylight savings time or not, and if it does when the clocks change.
This means there are some places with more locations than others included - for example in the US, there are some states which span two different timezones. Using Indiana as an example, Knox (which is in the Central timezone) and Marengo (in the Eastern timezone) both appear in the list even though they've only got a population of about 50,000 people between them - but the entire state of Texas (with 36m people in it) doesn't appear because it's all in the Central timezone, and the entire country of South Africa has just one entry of Johannesburg.
So, which should I pick if my home location doesn't exist?
The key thing is picking a location that matches your timezone. If you're in Cape Town and pick Africa/Johannesburg, the time calculations will come out right. If you're in Marseille and pick Europe/Paris, likewise - friendly national rivalry aside, your clock will change the same way, at the same time as the ones in Paris.
In some areas - in particular the US - this might mean working out the closest point to you. If you're in Fort Wayne, IN then you're closer to Marengo, IN which is in the same timezone as you than you are to Knox, IN or Chicago, MI. If you're a proud Texan, this is your opportunity to embrace your inner northerner and join up with the good folks of Chicago.