From Greenwich to The Mall by way of Tower Bridge and Docklands, the London Marathon crosses the city along the Thames, and its line is instantly recognisable.
MapRender is not affiliated with the organisers of this race. Import the trace your watch recorded, or the course GPX if the organisers publish one.
Sample running poster (West Highland Way) — yours follows your own trace
Import your race trace, add your time and — if you ran for a charity — its name: often the line that matters most.
Drop the file on the homepage and the layout composes itself around the course; then change anything — line colour, map style, race name, date, finish time, a dedication. The preview is free, and the 300 dpi PNG downloads for €9, ready to print from A2 down to A5.