The scientific paper or report is another type of one-way communication that can pack in more information. The reader can take as much time as they like reading and rereading the information. However, the author is not there to interact with the reader and answer questions.
Posters can be some of the most interesting and interactive ways to communicate science to various audiences. It is a two-way form of communication that integrates elements of both the scientific talk and the scientific paper. A good poster promotes dialogue between the presenter and the audience, which is contantly changing as people drift in and out of the conversation. A good poster should rely on graphics to tell a story. If people have to spend too much time reading your poster, then it is not well-designed.
Examples of past Macaualy posters can be found here:
http://eportfolios.macaulay.cuny.edu/seminar3posters/category/2014-posters/
Some good resources on science posters can be found on the Internet here (from North Carolina State University):
http://www.ncsu.edu/project/posters
and here: (from UC Merced):
http://graduatestudent.ucmerced.edu/jmatthews/Site/Designing_Effective_Research_Posters.html