arcgis desktop - Calculating proportional data for polygon by taking attributes from other polygon

I have a features class which has polygons in it. I also have a Block group level data for demographic variables like population. Now when I overlay the polygon on the block group level data to find out the population of that polygon.Now it would happen that the polygon boundary may not overlap exactly with the Block group boundary.It would intersect at different places with the block group data.

In such case how can you calculate the proportional population value to be considered for that polygon?

Answer

You'll want to to ensure that both of the layers are in the same Coordinate System.

1. 
   
   

   Add a new field in the BG Data, and calculate the area, bg_area.

   
   


2. 
   

   Run Intersect on your custom polygons and the BG data to create an intersection layer.

   
   


3. 
   

   Ensure that you have the area of your custom polygons calculated. Arc should automatically calculate this in Shape_Area.

   
   


4. 
   

   Create a new field in the intersection layer, weighted_population.

   
   
   


5. 
   

   Calculate that field by taking Shape_Area / bg_area * population = weighted_population.

   
   


6. 
   

   Dissolve your intersection layer on the Object ID's of the Custom_Polygons, and calculate a statistic field with the SUM of weighted_population.