When I begin a drawing, especially one modeled after a photo, I go into this with the understanding with myself that I am going to have to make some mid drawing adjustments.
This is one of the main reasons that I draw in detail with graphite first then come back and add coloring. I will do up to four layers of color on some objects, so it is absolutley critical that I have the right shapes. When I start to color in, I use my Verithins, the harder pencils, to add outlines and base color. The Verithins are easy to erase and blend as a base for other color.
Tower re-worked and projection lines adjusted.
The first drawing shows the tower in the background with the original configuration that I had drawn. Something kept nagging me and I took another look at the Chicago Trade building and realized I had the pattern wrong for the front of the building. Since I had drawn this in with the Verithins first, I had no problem erasing and adding in a new front. I then statred adding the softer Prismacolors with a blending solvent and a neutral blending pencil. Sometimes I will use the Verithin pencils of the same color as a blender.
As I complete the work, you will notice I work left to right and top to bottom, the undrawn area becomes more clear and I can make adjustments to projection (perspective) of the lines. I re-adjusted the contour lines of the Zephyr and the relationship of the platform, tracks and the train as it exits the terminal.
I will continue to refine lines and angles as I complete each section. This is what I mean when I say that I will have drawn this at least 4 times before I am finished.
I sometimes go at a snail's pace, or it seems that way to me, but I have learned not to rush even though I want to have it done. "now".