Bonjour :)
Je pense qu'il y a trop de répétition sur "there is/are".
Tu peux faire :
I can see a map of London and on its, there are many streets. On the map, there are black cabs and double-decker buses. On the left of the map, we see Buckingham Palace. On the map, there is a lot of monuments or famous places : theTower Bridge, the river Thames, Trafalgar Square, the Tower of London. I can see a Coldstream Guard (the queen's guard).
J'ai amélioré ton texte sinon pas de faute :)) Bonne soirée