Approach I

• 1). Acquire United States Geological Survey (USGS) topographic maps at 1:24,000 scale that cover the drainage network of interest.
  
  
• 2). Trace the drainage area of interest on the topographic map.
  
  
• 3). Outline the drainage area with a polar planimeter by moving the tracer point along the previously traced area.
  
  
• 4). Record the enclosed area in Vernier units.
  
  
• 5). Convert the Vernier units to the desired area measurement based on scale of map and conversions provided with the planimeter.
  
  

Approach II

• 1). Acquire United States Geological Survey (USGS) topographic maps at 1:24,000 scale that cover the drainage network of interest.
  
  
• 2). Trace the drainage area of interest on the topographic map.
  
  
• 3). Digitize the drainage area into a Geographic Information System (GIS) file using the GIS unit and the add-on digitizer.
  
  
• 4). Compute the drainage area using the accompanying software from USGS.
  
  

Approach III

• 1). Acquire United States Geological Survey (USGS) topographic maps at 1:24,000 scale that cover the drainage network of interest, and trace the drainage area of interest on the topographic map.
  
  
• 2). Place a sheet of 100 dot-per-square-inch transparent overlay on top of the drainage area on the USGS map.
  
  
• 3). Count the total number of dots falling within the drainage area and half of the dots falling on the lines.
  
  
• 4). Find the correct conversion factor, noting map scale. For a 1:24,000 scale, the correct per dot area conversion factor is 0.003889 kilometers (km) squared.
  
  
• 5). Calculate drainage area by multiplying the total number of dots by the conversion factor.