When the land was originally mapped, the parcel sizes were often chosen arbitrarily to meet certain long term city planning density projections. In many areas this does not equate to lot sizes for the houses, which many times have lots that are sitting on several legal parcels. There are blocks here in Point Loma where each 5000 sq/ft lot is actually 2 parcels 25×100. There are pockets in cardiff, leucadia, carlsbad and escondido that I know about, that are similar. Those are the golden properties if you are looking to build, as you can easily divide the lot along the parcel boundaries without having to subdivide, and have 4 houses where one used to stand, all without condoizing anything.

As far as the trust goes, there are several benefits when you are estate planning vs a std will. A trust will avoid probate costs and need of a court appointed conservator to transfer the property, is recognized across state boundaries which gets you out of multi state probate if you own RE in more than 1 state, and a trust is an entity and therefor maintains privacy of its assets. There is a lot more but those are the big ones.