  (Abridged) Surveys of protoplanetary disks in nearby star-forming regions
(SFRs) have provided important information on their demographics, but due to
their sample sizes, they cannot be used to study how disk properties vary with
the environment. We conduct a survey of the unresolved millimeter continuum
emission of 873 protoplanetary disks identified by Spitzer in the L1641 and
L1647 regions of the Orion A cloud. This is the largest such survey yet,
allowing us to identify even weak trends in the median disk mass as a function
of position in the cloud and cluster membership. The sample detection rates and
median masses are also compared to those of nearby (<300 pc) SFRs. The sample
was observed with ALMA at 225 GHz, with a median rms of 0.08 mJy/beam (1.5
M$_{\oplus}$). The data were reduced and imaged using an innovative parallel
data processing approach. We detect 58% (502/873) of the observed disks. This
includes 20 disks with dust masses >100 M$_{\oplus}$, and two objects
associated with extended dust emission. We infer a median disk dust mass in the
full sample of $2.2^{+0.2}_{-0.2}$ M$_{\oplus}$. In L1641 and L1647 median dust
masses are $2.1^{+0.2}_{-0.2}$ M$_{\oplus}$ and $2.6^{+0.4}_{-0.5}$
M$_{\oplus}$, respectively. The disk mass distribution of the full sample is
similar to that of nearby low-mass SFRs at similar ages of 1-3 Myr. We find
only weak trends in disk (dust) masses with galactic longitude and between the
YSO clusters identified in the sample, with median masses varying by $\lesssim$
50%. Age differences may explain these median disk mass variations. Apart from
this, disk masses are essentially constant at scales of ~100 pc. This also
suggests that the majority of disks, even in different SFRs, are formed with
similar initial masses and evolve at similar rates, assuming no external
irradiation, with disk mass loss rates of $\sim 10^{-8}$ M$_{\odot}$/yr.
