Yes, you've got it right. There's only the one grey city available at the start. You use the urbanisation action to decide where and when different coloured cities become available.
Enjoyed this map very much, I scored 34 points but was very lucky; only 3 black cubes during set-up and no black cubes drawn during the game. Hope to see more solitaire maps for Steam soon.
Recommended this map! It is a nice puzzle, but not too difficult. I scored 27 and 29 points. More is certainly possible with more luck of draw and set-up. My only comment would be that the map is not fully built yet after turn 8. The game could last for two more turns. Thanks for producing and uploading it. It is now ready to get a separate entree into the BGG-database, so it can be logged and rated (and easier found, so it gets more play). Do you take the honours yourself?