Many artists will use opaque pigments which allows them to make corrections in a transparent watercolor painting. Two of my favorite artists, Winslow Homer and John Singer Sargent used opaque paint with amazing results.
So if I do make a mistake in this section of the painting I could easily use opaque paint to correct it. However, for me the challenge is the beauty of transparent layers, the most important aspect of painting in transparent watercolor.
In an example from an older painting, you can see the concept of painting "through" objects instead of "around" objects. The first wash was painted freely without regards to edges..
As you recall, I left a hard edge in the previous step. There is not a great difference in this section from that section as far as depth is concerned, so the edge should be soft. In the last step I chose to "overpaint" the edge to soften it. In this section I softened the edge very lightly with water.
The next decision to make is how I will want to handle painting the edges of the structures. I want distinct but not hard edges on the sides of the buildings, and soft edges at the bottom, so that they look like they are "in" the ground instead of "on" the ground.
To do that I had to keep the bottom of each building wet and wait for the "sides" to dry enough so that the edge would be distinct. I will deal with the rooftops later.