Image resize problem

The document size area deals with the size of the image when printed.  Points, Pica, Columns are all terms printers use.  

Points, and pixels are pretty much the same.

If working on something specific, like a workheet I might use in school, I switch the document size to inches- simply because that's the way my brain works. 

Columns is actually a reference to how newpapers are layed out. Newspaper can be made to have five columns, six columns, seven and one-half columns, eight columns or nine columns. Newspaper can be made to have five columns, six columns, seven and one-half columns, eight columns or nine columns.

Points? Over time the value of a point has changed.  Today, with the advent of Desktop Publishing a point is 1/72nd of an inch.  It's where font sizes come from-- A 36 point font ins 1/2 inch tall.

Pica:  1 Pica is 12 points.  6 Pica to the vertical inch in commercial printing.  72 points to a verticle inch.