Differences between displacement map and topography map

Dear All,

  1. Single-pass InSAR systems (TanDEM-X) will be good for producing topographic maps and repeat-pass InSAR systems with a small baseline will be good for displacement maps.
    Note that the displacement disappears in single-pass InSAR systems.
    Am I right?
  2. If we want to know about the displacement, one interfrogram can be enough? When we use two interfrograms? Using two interfrograms is only for topography purposes?
  3. As I know topographic part and DEM has information about the hight but how about the displacement? As I read the displacement can show deformation in vertical and horizontal or combination of both.
    What is differences between topography and vertical deformation?