Also known asplot selectionbhoomi chayanchoosing land
Shilpa Ratna describes the types of land and their correction with minerals. Land holding asura (demonic) minerals, such as coal, lignite, manganese and other black minerals, lacks prosperity; placing gems inside such land (ratna prabha bhoomi) changes its chemistry and composition.
Inside the land of the plot
If your building is 16 feet high, a northern building up to 1 to 2 feet taller is acceptable, but one 4 to 5 feet or more taller, such as 20 feet, causes much harm. Distance removes the effect: a taller building or raised hill standing at least double your building's height away has no effect, so a 70-foot building is not affected by a building of double height 150 feet away.
From the deity. Imagine the deity seated facing out: do not live on the deity's own left side, while the deity's right side is very good. On either side your wall must not touch the temple wall; if you leave a gap and build your own separate wall there is no negative effect, though the right side still gives the better results. Many people living on the left, touching the temple wall, have been ruined.
No. With a road in between there is no defect.
It is bad. Where metallic minerals, and especially black ones such as coal, are plentiful, negative forces settle: mineral-rich Bihar and Jharkhand and diamond-bearing Panna district are not prosperous, because few people can bear such strong energy, just as a 400 carat neelam or 20 paracetamol harms instead of helping. Minerals at the surface act on the house directly, while metals bound with silicates or lying deep underground, as at the Kolar Gold Fields, are not as harmful.
There is no criterion for finding the centre; the centre is always the centre. The proportion matters for the plot itself: up to 1:1.5 is good (30 x 45 feet is ideal), up to 1:2 (30 x 60) is neither good nor bad, and longer than that is not good, with more loss the longer it gets. In such long plots many devtas fall outside or get cut, and they need treatment.
An L-shaped plot is inauspicious in the first place. There is no special formula for its ratio; estimate it from its arms. The cut portion is a full loss, and how harmful it is depends on which corner is cut, which is best judged with the teacher case by case.