I heard that 養屍地is the place concentrate lot of "YAM" air (about Fung Shui ), after屍體contact it....it will have 屍變 easilt...of course they will not chnage to 彊屍 directly (there are some processes still...some one say need a black cat jump over the屍體...and need thunder hit the ground...anyway.I don't believe most) ...but mostly 屍變's 屍體 not easy 腐化....I think this is the reason that the place there is very COLD and windy...which reserve a good temperature like freezer keeping the 屍體 in good condition..
of course, some religions state that 養屍地 is the most YAM and COLDEST place.....it's hard to find....I only heard there's few in HK...one is in Happy Village......the other I forget relaly...