Not an on the dynamic range
Sometimes the dynamic range of the scene – the difference in brightness between the darkest and lightest points – may be too wide for the camera sensor to cope with in a single exposure (see page 56 for more on this). The key to identifying this is to check the histogram: if it extends beyond both the left and right-hand ends of the graph, then exposure compensation won’t make any difference. This is typically the sort of situation you’d encounter when shooting a backlit portrait, or a landscape at dawn or dusk.
There are a variety of ways you can reduce the dynamic range of the scene so that it fits within the dynamic range of the camera’s sensor. These include using flash to brighten up a backlit portrait, or a attaching a graduated Neutral Density filter (ND grad) to darken a bright sky in a landscape shot, bringing its exposure level closer to that of the land. With stationary subjects you could also try taking two or more pictures at different exposures and then blending the best bits of each in software.
In this situation, you could either expose for the sky or expose for the buildings (top). One solution is to shoot two images and blend the well-exposed areas of each image in Photoshop later (bottom)