A type of perspective distortion caused by tilting the camera upwards to photograph tall buildings. It’s worse with wideangle lenses because they let you stand closer, so you tilt the camera even more. The only solution is to compose the shot with the camera completely level.
This the picture’s proportions as width versus height. DSLR sensors have a 3:2 ratio, so that photographs are 3 units wide to 2 units high. Most compact camera sensors have a slightly squarer 4:3 aspect ratio. It doesn’t matter what the units are – the ratio stays the same, so a photo could measure 3 inches by 2 inches or 6 meters by 4 meters and still have the same 3:2 aspect ratio. You can shoot in different aspect ratios by cropping the sensor area. HD video is shot in a wider 16:9 ratio.