NSString+Distance.h

//
//  NSString+Distance.h
//
//  Created by Alexander Johansson on 2011-11-27.
//  Based on http://stackoverflow.com/q/5684973/590396
// 

#import <Foundation/Foundation.h>

@interface NSString (Distance)

+ (NSString *)stringWithDistance:(double)distance;
// Return a string of the number to one decimal place and with commas & periods based on the locale.


+ (NSString *)stringWithDouble:(double)value;
@end

NSString+Distance.m

//
//  NSString+Distance.m
//
//  Created by Alexander Johansson on 2011-11-27.
//  Based on http://stackoverflow.com/q/5684973/590396
//

#import "NSString+Distance.h"

#define METERS_TO_FEET  3.2808399
#define METERS_TO_MILES 0.000621371192
#define METERS_CUTOFF   1000
#define FEET_CUTOFF     3281
#define FEET_IN_MILES   5280

@implementation NSString (Distance)

+ (NSString *)stringWithDistance:(double)distance {
    BOOL isMetric = [[[NSLocale currentLocale] objectForKey:NSLocaleUsesMetricSystem] boolValue];
    
    NSString *format;
    
    if (isMetric) {
        if (distance < METERS_CUTOFF) {
            format = _(@"%@ metres");
        } else {
            format = _(@"%@ km");
            distance = distance / 1000;
        }
    } else { // assume Imperial / U.S.
        distance = distance * METERS_TO_FEET;
        if (distance < FEET_CUTOFF) {
            format = _(@"%@ feet");
        } else {
            format = _(@"%@ miles");
            distance = distance / FEET_IN_MILES;
        }
    }
    
    return [NSString stringWithFormat:format, [self stringWithDouble:distance]];
}

// Return a string of the number to one decimal place and with commas & periods based on the locale.
+ (NSString *)stringWithDouble:(double)value {
    NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
    [numberFormatter setLocale:[NSLocale currentLocale]];
    [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
    [numberFormatter setMaximumFractionDigits:1];
    return [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];
}
@end

NSStringDistance.h

//
//  NSString+Distance.h
//
//  Created by Alexander Johansson on 2011-11-27.
//  Based on http://stackoverflow.com/q/5684973/590396
// 

#import <Foundation/Foundation.h>

@interface NSString (Distance)

+ (NSString *)stringWithDistance:(double)distance;
// Return a string of the number to one decimal place and with commas & periods based on the locale.


+ (NSString *)stringWithDouble:(double)value;
@end

NSStringDistance.m

//
//  NSString+Distance.m
//
//  Created by Alexander Johansson on 2011-11-27.
//  Based on http://stackoverflow.com/q/5684973/590396
//

#import "NSString+Distance.h"

#define METERS_TO_FEET  3.2808399
#define METERS_TO_MILES 0.000621371192
#define METERS_CUTOFF   1000
#define FEET_CUTOFF     3281
#define FEET_IN_MILES   5280

@implementation NSString (Distance)

+ (NSString *)stringWithDistance:(double)distance {
    BOOL isMetric = [[[NSLocale currentLocale] objectForKey:NSLocaleUsesMetricSystem] boolValue];
    
    NSString *format;
    
    if (isMetric) {
        if (distance < METERS_CUTOFF) {
            format = _(@"%@ metres");
        } else {
            format = _(@"%@ km");
            distance = distance / 1000;
        }
    } else { // assume Imperial / U.S.
        distance = distance * METERS_TO_FEET;
        if (distance < FEET_CUTOFF) {
            format = _(@"%@ feet");
        } else {
            format = _(@"%@ miles");
            distance = distance / FEET_IN_MILES;
        }
    }
    
    return [NSString stringWithFormat:format, [self stringWithDouble:distance]];
}

// Return a string of the number to one decimal place and with commas & periods based on the locale.
+ (NSString *)stringWithDouble:(double)value {
    NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
    [numberFormatter setLocale:[NSLocale currentLocale]];
    [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
    [numberFormatter setMaximumFractionDigits:1];
    return [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];
}
@end

Prefix.pch

// [..] all your stuff

#define _(localizedString) NSLocalizedString(localizedString, nil) // Preprocessor macro. Shortcut to translate strings.