Re: Thermal relief
The word "thermal" is used in two different contexts when talking about PCB layout. It isn't clear from your question which one you are asking about.
There are thermal reliefs which are thru-hole pads or vias with reduced copper contacts to the plane layers to reduce the amount of thermal energy (heat) necessary to solder and desolder components. You choose the number, angle, and size of the "spokes" depending on the current being carried, and the density of the components on the board. The more components you have, the less room there is for a thermal without isolating the connection from the rest of the plane.
There are also thermal pads which are used to conduct the heat of a component such as QFN IC packages to the copper of the PCB board for enhanced chip cooling. A thermal pad would not have thermal relief - it would be directly connected to a solid plane. This is because you want maximum heat conduction away from the device.