find the closest match to given latitude / longitude from data stored in 2 columns

Greetings,

I've run into a wall with this one, so I had to ask for help

I have 2 different sets of data: temperature data recorded at meteo-stations defined by latitude / longitude, and major world cities also defined by latitude / longitude.

After the user chooses the station's coordinates, temperature data is pulled out from the first data set; this works!
However, I would like to be able to provide information about the closest city to the chosen meteo-station from the second data set. This doesn't work, and I don't have a clue how to go about it.

Any good Samaritans out there? Please?
File attached with sample data sets.

Many thanks,
Florin