Sentence:  Old attitudes are held more tenaciously in the Tidewater than the Piedmont ; so that a line running down the <WSD>length</WSD> of the South marking the upper limits of tidewater would roughly divide the Old South from the new , but with , of course , important minority enclaves . 
Meaning of the word marked with <WSD> tags:  the linear extent in space from one end to the other; the longest dimension of something that is fixed in place