A point has zero dimension and a line has 2?

You are apparently referring to the Cartesian system of assigning x, y, and z coordinates to map out the relationship of objects in space.

a point has to occur somewhere - and to define its location in two dimensions (like in a floor plan) you need to provide an x and a y dimension. If you want to describe the location of a point in three dimensional space you also need to provide a height above the ground - the z coordinate.

A line is simply the direct path between two points in space. Thus, to draw a line you need two points.

If you are asking how to measure these with a ruler, a point has no dimension. A line has only 1 dimension.