Your plan is to go to Washington DC. You're 42 miles south of DC, so your distance from the target city is -42 You're 42 miles short
then you half fell asleep on the freeway, thinking about something else, missed your exit, and overshot your target, now you're +42 miles from Washington
Measure distances as plus or minus with Washington as the origin (0,0) on a graph. moving your location point from (0,-42) to (0,+42)