Say the coordinates (0,0) and (0,1) describe a line on a coordinate grid. If the second coordinate is in the vertical direction, this would be a vertical line from the origin to one unit up from the origin.
A line twice this length could have any pair of coordinates that differ by 2 in one of the directions. (That's not the only way to describe a line twice the length of our first line, but it is an easy way.) For example, the line between (0,0) and (0,2) would be twice as long as the first line.
The line described by the coordinates (4,6) and (6,6) would also be twice the length of the (0,0)-(0,1) line. (It would be a horizontal line.)
A line twice this length could have any pair of coordinates that differ by 2 in one of the directions. (That's not the only way to describe a line twice the length of our first line, but it is an easy way.) For example, the line between (0,0) and (0,2) would be twice as long as the first line.
The line described by the coordinates (4,6) and (6,6) would also be twice the length of the (0,0)-(0,1) line. (It would be a horizontal line.)