Module 3 Exercise 2: errors in Sierra Leone airports data

[ioalexei]

• The exercise says to find the feature with the name "Tongo airport", but there is no feature with this name in the data

• There is a feature with null coordinates that shows up at "Null Island"

• The dataset contains features from OSM that aren't relevant, e.g. aeroway=gate and aeroway=helipad (and none that are actually marked as airports)