The atlas used in JyotishTools apps are derived from the Geonames.org database. Most of this data is taken from census databases. The location in longitude and latitude of a “populated place” or city is usually the city hall or other administration building. People generally aren’t born at city hall and instead often a hospital which might be miles away from the city administration building. You can verify this with Google Maps and you should find a marker for the city over the administration building.
However the difference between that location and the actual birth location is usually not enough to change the ascendant much. The distance for one minute of longitude or latitude is 6,068 feet (1.15 miles). Note that longitude and latitude are only used to calculated the ascendant and not the position of the planets which is done by time zone offset.
Another issue which sometimes arises is a birth location that has been given is actually a district, borough or county. An example would be The Bronx in New York city which is actually a county. Currently the script which compiles the atlas omits districts, boroughs and counties. Including them would make for a much, much larger atlas which currently in some cases is larger the than app itself. Instead refer to the included city. And of course for greater precision one can use the Maps feature and even zero in on the hospital location if it makes any difference.
But remember, birth times are notoriously inaccurate too.