There have been a number of mapping tools created which explore scale and enable comparisons between places. I posted recently about the Ever Given Everywhere map which allows you to place the infamous container ship in a location of your choice. Thanks to Brendan Conway for the lead to this tool which also offers that option.
The Insizeor also allows you to draw around a shape or an area and then place a copy of that in any other location to compare the size.
Here, for example is the O2 arena placed next to Ely Cathedral.