The baseline method of documenting the location of evidence and clues is another simple procedure used by investigators all over the world and is mainly used for documenting land evidence. You simply start with two outside reference points that have all your clues and evidence somewhere in between or to one side.
If you don't have two good reference points to use you can make two of your own by using rebar (metal rod) or something similar. Secure a line (rope, string, etc.) or measuring tape between both references. This becomes your baseline and will remain in place while you are collecting the measurements for your sketch. Next, measure the distance between both references.
Then take a measuring tape to your first piece of evidence and measure the distance from the center of the evidence to the baseline. Here is where you have to be careful. This measurement has to be at a 90-degree angle to the baseline. To get this angle you will need to use a protractor, or you can move the extended end of your measuring tape along the baseline until it shows the shortest distance, at which point the tape will be at 90 degrees to the baseline.
After you get your right angle and measurement from the evidence to the baseline, measure from that point on the baseline to the closest reference point on the baseline. If you're using a second measuring tape as your baseline, simply record the measurement from the reference point to the point on the baseline tape. Be sure to note where the "0" point (starting point) is located on the reference point and which of the two reference points has the "0" end.
Then go to your next piece of evidence or clue and do the same thing. Make sure your records show which end of the baseline was used for the measurement and which side of the baseline the evidence was on.