Prepare for the sketch by observing and making note of any special features or evidence at the scene. Take any measurements you will need to make the drawing to scale. Make a crude outline of the area and mark the location of important details within that area.
Make notes that include the case number, names of people involved in the case, the scale being used and a key that explains the identifying information in your drawings. A compass rose that shows which way is north may also be helpful.
Use this information to draw a rough sketch of the crime scene. This entails a simple pencil outline that includes the location of important evidence and objects in the area. This sketch should not be drawn to scale yet, but you should include any measurements that were taken. Finish the sketch before anything has been moved and encompass as much detail as possible.
Complete the full sketch on the graph paper, including all evidence, measurements and points of reference at the crime scene. Use a protractor to indicate the exact measurements of any angles and a ruler to ensure the lines are straight.