A city notebook can hold impressions that a photograph alone would miss. A rough drawing records the arrangement of a corner, while a few words preserve why you paused there. The two forms do not need to repeat each other.
Choose a comfortable stopping place and sketch only the main lines of the scene. Mark a doorway, a change in pavement or the edge of a shadow. Leave detail out deliberately so the page remains quick enough to make during an ordinary walk.
Add a short description of the atmosphere and your viewpoint. Distinguish direct observation from interpretation, especially when writing about unfamiliar places. There is room for uncertainty in a useful notebook.
Later, choose one entry to develop into a longer piece. Keep the original page beside it so the writing remains connected to the initial observation. A modest record made with care can provide a stronger starting point than a more dramatic story reconstructed from memory.