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Country Code - This is taken from the ISO 2-letter country code standard. This will force any P-code to be recognized as text rather than a number, which has the advantage of being sure that leading zeroes are not dropped and reduces the risk of database key incompatibility. The country code is also useful if CODs are ever merged into one database as it will ensure P-code uniqueness.
Administrative level 1 to Administrative level x - Each administrative level receives a numeric code with enough leading zeros to ensure that the occasional addition of new administrative units will not exceed the number of codes available. In the example below, two digits are adequate for administrative levels 1 - 3 (meaning that there are not expected to be more than 99 administration units in any one of these levels). Level 4 can have as many as 999 administrative units.
Incremental Settlement Numbers (if required) - For simplicity of maintenance, it is best to use a single set of incremental numbers across the whole country (rather than within each administrative unit). This has the additional advantage of allowing places to be referred to using only the settlement number without the admin unit codes, making them shorter. Enough digits should be used here to allow for the possibility of new datasets to be added.
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