'deem' is more formal than 'consider'. They have the same meaning, but in conversation you don't hear 'deem' often unless it is in something more formal like a presentation or a speech. In writing, 'deem' is a little more common. In formal writing - journals, etc it is common, but even in newspapers you will see it. As well if you were writing a college level assignment, you may see 'deem' written as an alternative to 'consider'. Often in this sort of formal writing the two terms are mixed to avoid repetition of one.

to be deemed = to be considered The house flooding was deemed a total loss.