Originally (except for the original thirteen colonies) all land (except what became Indian reservations) belonged to the federal government with some land to the state governments as they were formed. That is specially true for lands involved in the Jefferson Purchase. The section, township, range system was developed to identify those lands. Then when the Homestead Act went into effect--settlers would claim their home steads which were identified by a proportional section of a square mile (section), township and range (distance from the central point in the state) and unless a mining claim, river, location along the extreme north and west of the township and range then government lot numbers would be assigned. That identification became the legal description known today and what every legal description since is based on and is known as the Public Land Survey System. The slang term metes and bounds is used to describe that but technically a metes and bounds legal description is what exists in the original thirteen counties (west 13 chains to the cherry tree, south to the Jone's property, east to the creek, north to the big rock). Eventually an enterprising person would sell some of their land, new legal descriptions for each split would then be filed in the county recorder or clerk or parish office. Some very enterprising souls would decide to create a subdivision. That area would then be surveyed and lots/blocks, etc would be platted out. Then the lot/block, etc would become the legal description for that specific small parcel. Any thing that has NOT been subdivided in the past 200 years is described by a "metes and bounds" legal description. So if you are in an area that has been mostly subdivided you will have legal descriptions similar to this: Lot 12 Block 5 Phase Sunnydale Place, town of Anywhere, Any County, Any state. In your appraisal report you would type Lot 12 Block 5 Phase Sunnydale Place. Some underwriters in the Phoenix area use to insist that MCR # had to be added (which really is not necessary), that represents Maricopa County Recorder plat number, where it was filed in the recorder's records.
The areas that have not been subdivided would have legal descriptions that could be very simply like the Northwest Quarter of the Southwest Quarter of the Southwest Quarter of the Northeast Quarter of Section 21, Township 27 East, Range 9 South of the Gila and Salt River Meridian, Graham County, Arizona. Or you might have a legal description that has been surveyed and goes into great detail with degrees, minutes, seconds, spiral curves, etc, etc, etc, etc. This is the type of legal description I strongly recommend you provide a copy of the recorded document obtained from the county recorder/clerk/parish office or your client (if you attempt to type it--there is room for error). That way you know exactly what you are appraising which might be completely different than what is currently in assessor's records. By the way the proportionate description I quoted above means the property is located 54 miles south, 162 miles east of Phoenix International Raceway southwest of Phoenix (the initial point for every legal description in the state of Arizona is on a hill overlooking the NASCAR track). The recorded plat of each subdivision has a "metes and bounds" description for the boundary.