Draw the horizon you actually have
A small sketch of trees, roofs and nearby lights can explain more about a missed view than another target list.
A sky chart can show an object above the astronomical horizon while a nearby roof keeps it completely out of sight. Recording the outline of your real observing place helps close the gap between a chart and an ordinary garden or courtyard. The drawing is a practical field note, not a precise survey.
Make the sketch before it is dark
Visit the intended spot while you can clearly see the route, ground and surroundings. Confirm that you are allowed to be there at the planned time. Choose a stable, accessible position where looking up does not mean standing in a roadway, blocking a path or leaning over an edge.
Sketch the outline of nearby buildings, trees and any other obstruction. Mark the broad directions using a method you can verify, and note how you established them. A rough outline is enough to distinguish a clear opening from a section that is blocked. Do not label an uncertain direction as a measured bearing.
Add the lights that change the view
Mark lamps, illuminated windows or other local light sources relevant to the spot. Note whether they are steady or change during the evening. The Canadian Space Agency's stargazing guidance discusses the effect of light pollution and the value of a darker observing location. Your sketch can show the smaller, local details that a regional map misses.
Use only permitted, considerate changes to your own lighting. Do not move into an unsafe or unauthorised place just to hide a lamp behind a wall. An imperfect view that you can access comfortably is a more useful starting point than an attractive location you cannot responsibly use.
Connect one observation to the outline
During a night-time session, choose a visible subject and draw its approximate position relative to a recognisable part of the horizon. Add the time and date. If using a sky chart or app, check its location and time settings, then compare the broad direction rather than expecting a flat sketch to behave like a complete sky model.
When something is not visible, distinguish the possible reasons. It may be behind a building, below the relevant part of your view, covered by cloud or simply not identified. Write what you know and leave the rest as a question.
Keep the map local and revisable
Return to the sketch as the season or surroundings change. Trees gain or lose leaves, and a different permitted position may open another part of the sky. Make a dated revision instead of silently changing the first drawing.
If you share the page, remove private addresses and other unnecessary location details. The useful information is the relationship between the observer, the obstructions and the view. A modest horizon sketch makes future planning more realistic because it begins with the sky you can actually reach.
Background: Canadian Space Agency: stargazing tips. The horizon-sketch method is editorial.