Set unitStyle to one of .Default, .Abbreviated, .Full:

formatter.unitStyle = .Full
var answer = formatter.stringFromDistance(distance)
// "150 feet"

formatter.unitStyle = .Abbreviated
answer = formatter.stringFromDistance(distance)
// "150 ft"

Objective-C

formatter.unitStyle=MKDistanceFormatterUnitStyleFull;
NSString *answer=[formatter stringFromDistance:distance];
// "150 feet"

 formatter.unitStyle=MKDistanceFormatterUnitStyleAbbreviated;
 NSString *answer=[formatter stringFromDistance:distance];
// "150 ft"