Sometimes given a photo, you want to (1) generate a smaller version of the photo and (2) crop it so it has a specific dimension, preserving it's aspect ratio and display the photo¹. The code to do this separately isn't difficult and there are many versions of it available online.

So you can either do:

(1) Crop then (2) Resize

or

(2) Resize then (1) Crop

Intuitively, it might seem there isn't much of a difference, but if you factor in the fact that iPhones (as of iPhone 6 Plus) can shoot panoramas as big as 43 megapixels or ~11-12 MB, choosing the right approach reduces the chance of crashing due to running out of memory.

With some profiling, you'll find that generally, it's better to do:

(2) Resize then (1) Crop

[1] You can't always do a resize, skip the crop, utilizing contentMode=contentUIViewContentModeScaleAspectFill because you might want to process the result, say with a mask.↩

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