Light Weights
Radius of Earth = 6378.1km. Assume R is radius of Earth + elevation
of city. If R is large then W is small. If R is small then W is
large. Here are the elevations of some Olympic Games host
cities:
Athens - 338m
St Louis - 142m
London - 24m
Mexico City - 3930m
The highest cities in the world are La Rinconada, Peru (5100m) and
Wenzhuan, China (5019m).
The difference in heights does not radically affect R.
Let m = 200kg and define significant as weight varies by less than
0.01N.