  The Magellanic Mopra Assessment (MAGMA) is a high angular resolution CO
mapping survey of giant molecular clouds (GMCs) in the Large and Small
Magellanic Clouds using the Mopra Telescope. Here we report on the basic
physical properties of 125 GMCs in the LMC that have been surveyed to date. The
observed clouds exhibit scaling relations that are similar to those determined
for Galactic GMCs, although LMC clouds have narrower linewidths and lower CO
luminosities than Galactic clouds of a similar size. The average mass surface
density of the LMC clouds is 50 Msol/pc2, approximately half that of GMCs in
the inner Milky Way. We compare the properties of GMCs with and without signs
of massive star formation, finding that non-star-forming GMCs have lower peak
CO brightness than star-forming GMCs. We compare the properties of GMCs with
estimates for local interstellar conditions: specifically, we investigate the
HI column density, radiation field, stellar mass surface density and the
external pressure. Very few cloud properties demonstrate a clear dependence on
the environment; the exceptions are significant positive correlations between
i) the HI column density and the GMC velocity dispersion, ii) the stellar mass
surface density and the average peak CO brightness, and iii) the stellar mass
surface density and the CO surface brightness. The molecular mass surface
density of GMCs without signs of massive star formation shows no dependence on
the local radiation field, which is inconsistent with the
photoionization-regulated star formation theory proposed by McKee (1989). We
find some evidence that the mass surface density of the MAGMA clouds increases
with the interstellar pressure, as proposed by Elmegreen (1989), but the
detailed predictions of this model are not fulfilled once estimates for the
local radiation field, metallicity and GMC envelope mass are taken into
account.
