The Standard Point Location Code (SPLC) is a system used to identify and locate points (cities, towns, villages, communities, railroad stations, etc.) used for transportation purposes in North America. The code is a unique nine-digit number that uses a system of nesting recognized political entities, such as States and Counties, and numbering them in a standard geographic pattern. The first six digits of the code identify the state, county, and city, while the last three digits (known as the Sub-Code) are used to further define a location within a city or town. Sub-Codes are assigned in groups of three digits for specific purposes, such as identifying parts of a city, colleges, universities, and military facilities, and are reserved for use by SPLC subscribers for their internal use to define locations specific to their own needs.

Each point is identified by a nine-digit number. For U.S. and Canadian points, the nine-digit number may be broken down as follows:

• The first digit of the code identifies a region;
• The first and second digits of the code identify a State, Province or Territory, or a defined portion thereof;
• The third and fourth digits of the code identify the county, or its equivalent, as part of the area covered by the first two digits. When taken together, the first four digits of the code provide a unique number for each county, or its equivalent, or a portion thereof;
• The fifth and sixth digits identify a point as part of the area covered by the first four digits of the code; 
• If the seventh, eighth and ninth digits are 000, the point is not defined beyond the City level. If the seventh, eighth and ninth digits are other than 000, the point is defined at the Sub-Code level (see Sub-Code Structure below).

When taken together, the entire nine digits provide unique codes for points as defined above.
For Mexican SPLC,

• The first digit of the code identifies a region;
• The first, second, and third digits of the code identify a state; 
• The fourth, fifth and sixth digits identify a point within a municipio as part of the area covered by the first three digits of the code; 
• If the seventh, eighth and ninth digits are 000, and the point is not defined beyond the City level. If the seventh, eighth and ninth digits are other than 000, the point is defined at the Sub-Code level (see Sub-Code Structure below).

When taken together, the entire nine digits provide unique codes for points as defined above.

Sub-Code Structure

To identify locations requiring definition beyond the city level, as defined above, the last three digits of the SPLC, known as the Sub-Code, are changed to a value other than 000. The Sub-Code consists of the last three digits of the SPLC and is assigned in conjunction with the first six digits of the SPLC. Certain groups of three-digit Sub-Codes are reserved for use as follows:

For example, Boston, MA, is assigned nine-digit SPLC 142000000. Locations within Boston needing further definition would be assigned a nine-digit code, the first six digits of which would be the same as Boston's code, to which the last three digits are changed to a value other than 000. Example: Dorchester Center located within Boston needs further definition (last three digits other than 000)

142000017-Nine-digit code assigned Dorchester Center, for example.
142000 -The “base” Is the first six digits Is the existing code for Boston.
017 -The three-digit “Sub-Code” Is added to the Boston code to further define.
142000017-Taken together, the entire nine digits define Dorchester Center with a unique code.

NOTE – Currently there are no rail station Sub-Codes.