Calculate area within polygons

[RitaRosvoldaune]

Hi,
I'm a new beginner to this, so please bare with me.

I'm calculating inundated area within a certain case study site to various flooding intervals. It was OK with number of buildings and length of roads, but I have problems with land use (industrial area, populated area etc).

1. First I clipped the land use shape file with the study area so I only had the land use within designated area.
2. I used this layer to clip with the the flooding intervals
3. Used Calculate Field, and everything looked fine in the dbf file where I found info on area flooded.

BUT, then I wanted to calculate % flooded in relation to the various land use categories within the study area. In the attribute table of the clipped land use layer it says SUM AREA for each variable (industrial area, populated are etc), is that the same as area within the designated case study area? I thought it would be a column called 'AREA'. the numbers don't make sense!

[TerryGiles]

If you're working with shapefiles, then you need to recalculate the area after each clip as they do not have any auto-updated area field like a featureclass in a geodatabase does.  For example -
Say you have a residential polygon in the full landcover data with an area of 100.  You clip it with a flood area that cover 1/2 of it - the area of the new polygon is 50, but the AREA field in the shapefile will still say 100.  If you right click on th AREA field in the table window & select Calculate Geometry, you can then get it to update the field to the correct area.  I would also run calculate geometry before starting anything, just to make sure what's in the full landcover data is also correct.  Another option would be to do all of your processing in a geodatabase and use the automatically created & updated Shape.Area field in your calculations.