It is asymmetrical with the thick side facing down to conform with the contour of the tub wall, and is held in place by pressure created by tightening those chrome screws.  

If you install it over the plywood without filling those low spots eventually the floor will contour to the shape of the floor and show those low spots.

You can also check out the city maps, click on the layers tab, scroll down to land base and when you're zoomed in enough on the map the tab for contours will pop up.

Instead of 2 x 2 cedar balusters, I've selected contoured wrought iron balusters that will be attached to the 2 x 4 cedar rails.

Huge pine trees, lakes and good contour.

Contour of the land away from the foundation.

Fence installers typically follow the contour of the ground to maintain the height.  

Bryan, most larger cities and counties where watershed is a problem will not allow you to change the contour of sites other than for limited structural improvements, like digging the foundation and packing the dirt around the structure for dranage away from the building.

I will most likely be putting down sheet vinyl to follow the contour of the floor and will adjust the base moldings for the changing floor heights.

@Tony C.You can try Contour Mortgage or Citizens Bank.