I believe you would have to create a new column and input the command to calculate what you are wanting. You could try the following:

case when "DNAME_2006" IN ('MASINDI') THEN ("Area_1" / "AREA") * "Population" END

UPDATE:

Unfortunately, I don't think you can do a simple SUM using the Field Calculator. However, there are a couple of other methods you could use (which are practically the same):

• Vector > Analysis Tools > Basic statistics

First open the attribute table, select whatever fields you want calculated and open the Basic statistics function. Select your layer, check the Use only selected features option and set the target field (in your case, "PopPerc"). Click OK and you will get the statistics including the SUM value.

• Install the Statist plugin

This is very similar to the above method except now you can toggle between windows which you couldn't do with method 1 (you had to close the Basic statistics function to change the selected fields). Personally I prefer this method because of the fact that you can quickly toggle, select various fields and run it immediately. The same setup applies here with selecting the layers, fields etc.

And you can get pretty graphs!

I believe you would have to create a new column and input the command to calculate what you are wanting. You could try the following:

case when "DNAME_2006" IN ('MASINDI') THEN ("Area_1" / "AREA") * "Population" END

UPDATE:

Unfortunately, I don't think you can do a simple SUM using the Field Calculator. However, there are a couple of other methods you could use (which are practically the same):

• Vector > Analysis Tools > Basic statistics

First open the attribute table, select whatever fields you want calculated and open the Basic statistics function. Select your layer, check the Use only selected features option and set the target field (in your case, "PopPerc"). Click OK and you will get the statistics including the SUM value.

• Install the Statist plugin

This is very similar to the above method except now you can toggle between windows which you couldn't do with the above method (you had to close the Basic statistics function to change the selected fields). Personally I prefer this method because of the fact that you can quickly toggle, select various fields and run it immediately. The same setup applies here with selecting the layers, fields etc.

And you can get pretty graphs!

I believe you would have to create a new column and input the command to calculate what you are wanting. You could try the following:

case when "DNAME_2006" IN ('MASINDI') THEN ("Area_1" / "AREA") * "Population" END

I believe you would have to create a new column and input the command to calculate what you are wanting. You could try the following:

case when "DNAME_2006" IN ('MASINDI') THEN ("Area_1" / "AREA") * "Population" END

UPDATE:

Unfortunately, I don't think you can do a simple SUM using the Field Calculator. However, there are a couple of other methods you could use (which are practically the same):

• Vector > Analysis Tools > Basic statistics

First open the attribute table, select whatever fields you want calculated and open the Basic statistics function. Select your layer, check the Use only selected features option and set the target field (in your case, "PopPerc"). Click OK and you will get the statistics including the SUM value.

• Install the Statist plugin

This is very similar to the above method except now you can toggle between windows which you couldn't do with method 1 (you had to close the Basic statistics function to change the selected fields). Personally I prefer this method because of the fact that you can quickly toggle, select various fields and run it immediately. The same setup applies here with selecting the layers, fields etc.

And you can get pretty graphs!