Any way to bold part of a NSString?

As Jacob mentioned, you probably want to use an NSAttributedString or an NSMutableAttributedString. The following is one example of how you might do this.

NSMutableAttributedString *string = [[NSMutableAttributedString alloc] initWithString:@"Approximate Distance: 120m away"];
NSRange selectedRange = NSMakeRange(22, 4); // 4 characters, starting at index 22

[string beginEditing];

[string addAttribute:NSFontAttributeName
           value:[NSFont fontWithName:@"Helvetica-Bold" size:12.0]
           range:selectedRange];

[string endEditing];

What you could do is use an NSAttributedString.

NSString *boldFontName = [[UIFont boldSystemFontOfSize:12] fontName];
NSString *yourString = ...;
NSRange boldedRange = NSMakeRange(22, 4);

NSMutableAttributedString *attrString = [[NSMutableAttributedString alloc] initWithString:yourString];

[attrString beginEditing];
[attrString addAttribute:kCTFontAttributeName 
                   value:boldFontName
                   range:boldedRange];

[attrString endEditing];
//draw attrString here...

Take a look at this handy dandy guide to drawing NSAttributedString objects with Core Text.