Satipatthana is vipassana bhavana, or mental development.  One of the conditions and support for the arising of satipatthana is sampajanna.  Sampajanna means to know what is good for you and what isn't, what is beneficial and what is less suitable for your accumulations.

 
As Khun Sujin explained and if I remember correctly, sampajanna precedes as well as supports satipatthana.  Sampajanna is defined as clear and thorough comprehension in all areas. There are four kinds of sampajanna, as follows:

1.  Satthaka-sampajanna is clear comprehension of what is good for you and what is not. Without knowledge of the beneficence of the dhamma, panna and particularly satipatthana, one would never even begin to study the characteristics of realities as they truly are.

2.  Sappaya-sampajanna means to know what is convenient and beneficent.  In one of the commentaries, seeing the chedi of a temple (in India) had been conditions for thousands of bhikkhus to attain stages of enlightenment.  On hearing this many would rush there and try it out.  They forget the bhikkhus LIVE where they see it daily.  The commentary also says that during festivals when the townspeople flock there, it might not be the sappaya for some.  Can we just be where we are and have sappaya-sampajanna? Right now there are conditions for us to be here in front of the computer screen.  Can we study realities as they appear?  Does location really matter?

It also depends on the individual's accumulations and level of understanding.  In the Sutta there is a story about a bhikkhu who took a samanera to town to get a toothbrush, when the samanera went ahead and saw a corpse.  He studied and attained a level of ariya-puggala there in the streets.  The bhikkhu saw him standing there and called him.  The samanera wanted help the elder, so he went back and told the bhikkhu to go to look at the same place, while he waited where he was.  The bhikkhu saw the same corpse and attained his level also.  Yet it is doubtful that this sort of thing is suitable for people in general, nor that it would be easily found in modern streets.  On the other hand, how would one really know if it hasn't happened?  Whatever comes can be studied, therefore all arammana can be convenient and beneficial with right understanding.

 3. Gojara-sampajanna is to know where one can find knowledge of things as they really are.  Gojara means the place one travels or one is in.  Since all the arammana one ever experiences could only arise through the six dvara, which are also the places sati arises, once we have this sampajanna knowledge, we have one more condition for sati and understanding of deeper kinds to arise and to continue to arise.

 4. Asammoha-sampajanna (a-sam-moha = not- with-moha or wrong understanding) is to know the difference between ignorance and right understanding, an essential prerequisite for panna that sees things as they really are.  This is where satipatthana arises.