calculating area

 I am a psychology student who has been using R to analyze experimental data
mainly within the general linear model for about 2 years.  I have some
working knowledge with R, but by no means would call myself proficient so
bear with me.  Currently I'm running a series of experiments dealing with
spatial data.  I'm tracking peoples movements using gps units which give me
latitude, heading, longitude, speed, altitude, and time variables.  I have
been using the packages "maps" and "mapproj" to plot the routes which these
individuals take which is a great visualization tool.  I would like to know
if there is a package or set of commands which would calculate the area
these people occupy?  So far the closest I have been able to get to
accomplishing this task is basically taking the max and min for both lat and
long coordinates and calculating the size of that area, but I would like
something more accurate.

  Another thing I'm trying to accomplish is creating
what I would call a density map. This is probably not the correct term so
let me explain what I mean.  I'm trying to characterize how people occupy
space.  Especially how people visit certain places more than others.  Is
there a way to create a map which shows the amount of times a particular
place is visited by these people both within subjects and a second map
between subjects? Help would be greatly appreciated, as my academic advisors
know next to nothing about working with this type of data.

Pedro

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