I found this map on the website http://mappery.com/ , and also http://mappery.com/city-maps-London, and http://mappery.com/Trafalgar-Square-Map.
What I like about this map is that it shows, in a general way, the roads into the neighbourhoods that surround the great square. It also offers some very practical information. There are many things missing, such as public washrooms, and the coffee shop that are located on the north side of the main plaza, in the heart of the Square. An important 'Legend' omission is that the little red dots represent bus stops. to get details, check TFL area map pdf; http://www.journeyplanner.org/Download/EnvMaps/tfl/TK_CharingCross.pdf