Here is some more encouragement to keep on sketching. People love to buy cards of places they have visited. There are a number of websites which allow you to upload artwork and then sell it on as prints, posters tee shirts etc. I have been using Redbubble for the past couple of years which is popular amongst photographers and mostly amateur artists. My Redbubble portfolio is linked below.
Peter LT. Edinburgh- and this is of course a sketch of the incomparable Edinburgh Castle skyline on a wet day.