Very straightforward: take one pic of something like a building, standing some way back with the longest focal length available so that it fills the frame.
Like so:
Then, with the lens set to the widest angle it can be, move closer to the building until it fills the frame again and take another picture. Like so:
I couldn't get any closer because I'd have got run over by the speeding traffic but this makes the point amazingly - what a massive amount of vertical distortion! Top tip is I guess stand as far back as possible to take pictures of this sort. Although, having said that, there is that lovely Remove Vertical Distortion tool in Elements which can help sort some of this stuff out, except that you do lose the edges - not always desirable.
