Spot metering for landscape photography was pioneered by Ansel Adams and his ‘Zone System’ back in the 30s. It is still applicable today, in the digital age, with a slight simplification.
Firstly, let us understand how your camera’s in built meter works. It is designed to give you a ‘middle grey’ tone regardless of the darkness or lightness level of the subject it is metering. Here, it can and most certainly does underexpose or overexpose a subject…anything that is not the middle grey tone would be metered off as below –
As you can see above, this is what your camera meter tends to do if you follow it blindly. Ansel Adams divided the different tones that are captured by film, into 10 zones, zone 1 being absolute black, zone 10 being absolute white, and zone 5 being the ‘middle grey’ with 18% reflectance value. Every zone is separated by a one stop exposure value. Now, film had much more exposure latitude value. For digital sensors, zones 3-7 are all we need bother about, with zone 3 and anything lower appearing pitch black, and 7 and above pure white.
Can you identify the 5 zones below?
Imagine the spot metering was taken off zone 5 here. What would be the difference if the reading was taken from zone 3 instead? can u imagine the shift in tonal values with the image becoming high key? There is no right or wrong to it, its only a matter of creative metering!