How to "square up" a lot.
How to square a parking lot before layout
All of your measurements should relate to one line - your base line. Choose the placement of this line carefully. Maybe if you have a long straight curb, you can use this as your base line. If the parking lot serves a building, make sure that the parking spaces will be square and parallel to the building. Once you have a base line, you need to turn a line at 90 degrees to this line. Here’s how we do it:
Once you have your base line, go ahead and lay out the ends of the parking spaces. In this case they are all at 9 foot intervals. Select a mark to use as your center mark, count an equal number of marks on either side, and use your long tape to draw an arc roughly at right angles to your base line. Snap a line from your center mark through the point where the arcs intersect. This line will be at 90 degrees from the base line. The longer the lines used, the more accurate the right angle will be.