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Glossary of Useful Terms


The main measurement of area used in the US. One acre is 43560 square feet, encompassing a rectangle 208.71 feet square. In Texas and parts of the adjoining states, two other area measurements may still be found: the league and the labor. A league is equivalent to 4428 acres, and a labor is 177 acres.

Aliquot part

The standard subdivisions of a section, such as a half section, quarter section, or quarter-quarter section.

Assessor's Parcel Number (APN)

A code number used to describe a parcel of land. It usually consists of a numeric code in three parts, for example 123-234-45, representing book-page-lot (see Chapter XX for more information)

Assessor's Parcel Map

Often described as a Plat Map. A map of a town, section or subdivision indicating the location and boundaries of individual properties.

Base line

A parallel of latitude, or approximately a parallel of latitude, running through an arbitrary point chosen as the starting point for all sectionalized land within a given area.


Having to do with the boundaries of land parcels.

Department of Environmental Health (DEH)

The County Department responsible for approving sewer or septic service to a lot

Government lot

A subpart of a section which is not described as an aliquot part of the section, but which is designated by number, for example, Lot 3. A lot may be regular or irregular in shape, and its acreage may vary from that of regular aliquot parts. These lots frequently border water areas excluded from the PLSS.

Initial point

The starting point for a survey.

Land grant

A land grant is an area of land to which title was conferred by a predecessor government and confirmed by the U.S Government after the territory in which it is situated was acquired by the United States. These lands were never part of the original public domain and were not subject to subdivision by the PLSS.

Marking corners

Lot corners have to be marked in order to provide a reference to the physical location of the lot. Corners are usually marked with metal disks called pins. The first thing a surveyor will do when asked to mark the corners of a lot is to look for the pins using a tool called a pin finder, a special metal detector. If the corners have not been marked or the pins cannot be found, a record of survey may have to be done.

Plat map

Often described as an Assessor's Parcel Map. A map of a town, section or subdivision indicating the location and boundaries of individual properties.

Principal meridian

A meridian line running through an arbitrary point chosen as a starting point for all sectionalized land within a given area.

Public domain

Land owned by the Federal government for the benefit of the citizens. The original public domain included the lands that were turned over to the Federal Government by the Colonial States and the areas acquired later from the native Indians or foreign powers. Sometimes used interchangeably with Public lands.

Public lands

Lands in public ownership, therefore owned by the Federal government. Sometimes used interchangeably with Public domain.

Public Land Survey System (PLSS)

A way of subdividing and describing land in the United States. Also called the Government Survey.


A vertical column of townships in the PLSS.

Record of Survey (ROS)

A record of the positions of the corners of a lot which has to be filed with the County Surveyor. If existing corners are not marked, or the pins have been lost, a new record of survey may have to be performed.


A one-square-mile block of land, containing 640 acres, or approximately one thirty-sixth of a township. Due to the curvature of the Earth, sections may occasionally be slightly smaller than one square mile.

Slope Analysis

A calculation of the average slope of a lot.  Usually done on topological map data using a computer program

Tentative Parcel Map (TPM)

A map required for all land divisions for four or fewer parcels or for five parcels if the fifth parcel contains the "remainder" which is not to be sold, leased or financed.


An approximately 6-mile square area of land, containing 36 sections. Also, a horizontal row of townships in the PLSS.



This website has been written and developed by Rob Ransom, PhD. Rob has extensive experience working with buyers and sellers of vacant land in San Diego County, CA. Although Rob currently has a California real estate license he is retired from selling real estate.

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