# Calculating the proportion of area drawn over boundary file

I'm working with agriculture area data in MapInfo. I downloaded the boundary file from StatCan (call it STC), and a freehand draw tool downloaded here https://tinyurl.com/ydarsnq8 (call it DRW)

I can draw an area (DRW) over the StatCan boundary file (STC). In some cases DRW falls over 2 or 3 regions (polygon) in the STC (call it STC1, STC2, STC3...etc)

How can I calculate the proportion DRW over each STC regions (i.e. DRW/STC1, DRW/STC2..etc)

Reason, each STC has a unique 'production' value and I need to compute the 'production' value for my DRW.

## 1 Answer

I have created two TAB files in Mapinfo - Poly1 and Poly2. Each TAB file has an attribute "Area". Poly2 has an attribute "poly1_area".

To calculate the proportion of Poly1 in the Poly2 table, Go to the Table Menu, then click on Update Column...

Table to Update: Poly2

Column to Update: poly1_area

Get Value from Table: Poly1

Calculate: Proportion Sum

of: Area

Click the Join button and specify where object from table Poly1 intersects object from table Poly2. You can choose whatever you need here.

Map: Poly1 (black), Poly2 (red):

Poly1 browser:

Poly2 browser:

Calculating the proportion is a matter of dividing poly1_area by Area.

• thanks for the feedback! quick Q: what version are you using? currently using 8.5 and looking to upgrade. – coolintake Jan 16 '18 at 15:47
• That was version 15. – Fezter Jan 16 '18 at 18:38
• in the first step of your solution (apologies, total newbie), how do I create .TAB files? When I upload the shapefile I can view the Table for the boundary file, but when I use the draw tool to draw the polygon on top, not sure how to view/create a Table for that shape...riding the struggle bus here – coolintake Jan 17 '18 at 15:59
• Please ask this as another question. Comments aren’t meant for extended chat and further questions – Fezter Jan 17 '18 at 18:57