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How to calculate percentage of a study area for land cover change?

__17

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

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Accepted answers

DanPatterson_Retired

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

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MichaelGinzburg

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

__17

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?

AbdullahAnter

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

__17

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.

DanPatterson_Retired

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

AbdullahAnter

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.

__17

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

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