I'm trying to calculate percentage of the study area that's under land cover change from 2001 to 2011. Would I add a new field and then go to field calculator and divide NLCD2001 and NLCD2011 and multiply by 100? Or am I missing a step and have to do something else instead?
Does anyone know how I should do this? Thank you
Solved! Go to Solution.
Newest date value minus oldest date value is the difference that occurred over time... time moves forward.
This difference, divided by what it was, (expressed as a percentage) is the change that occurred over time
Hello,
You are correct regarding adding a new field and calculating with the Field Calculator.
The whole process:
How To: Calculate the percentage of area for polygons
Add another new Double field, 'Percentage', and run the Field Calculator where 'OrigArea' is the original Area field from the 'county' layer:
[OrigArea] / [InterArea] * 100
Okay thank you! So in this case based on the information in my attribute table, would I plug in [NLCD 2001] / [NLCD 2011] * 100 in the field calculator?
If the values in your fields ( NLCD2001 and NLCD2011) represent the area of land cover. The percentage of change should to be calculate as the following:
( (NLCD2011 - NLCD2001) / NLCD2001 ) * 100
Okay thanks! I'm wondering why did you plug in NLCD2011 before NLCD2001 if the order is the opposite in the attribute table? Also, why did you divide it by NLC2001? Could you explain this for me please? I'm just trying to understand all of this. Thanks again.
Newest date value minus oldest date value is the difference that occurred over time... time moves forward.
This difference, divided by what it was, (expressed as a percentage) is the change that occurred over time
Y2011 - Y2001 = the change in ten years period
and this value will divide by Y2001 to know the change value relative to the previous status (Y2001)
finally multiply by 100 to get the change percentage % within 10 years
Also you can divide all that by 10 to get yearly change percentage.
I entered that equation you mentioned and it shows these numbers as the percentages in the attribute table. Is this correct? Like are these percentages supposed to be very high?
Thanks
Because I'm trying to get the percentage of the total study area under land cover change.
hmm.. you will do some thing else.
you will add two fields one for year2001 and the other for year 2011
then in Year 2001 field you will divide NLCD2001 by the total of study area ( use statistics for COUNT field and get the Sum ).
then do the Previous step with new field Year 2011.
the Equation will be same but change to new fields
( (Year2011 - Year2001) / Year2001 ) * 100