Page 11 - World Reference Base for Soil Resources of Thailand

Land Development Department Library

3.2 Rules for creating map legends

The following rules apply:
1) A map unit consists of
 a dominant soil only or

 a dominant soil plus a codominant soil and/or one or more associated soils
or

 two or three codominant soils or
 two or three codominant soils plus one or more associated soils. Dominant
soils represent ≥ 50% of the soil cover, codominant soils ≥ 25 and < 50% of the soils cover.

Associated soils represent ≥ 5 and < 25% of the soil cover, or are of high relevance in the
landscape ecology. If codominant or associated soils are indicated, the words ‘dominant:’,

‘codominant:’ and ‘associated:’ are written before the name of the soil; the soils are separated
by semicolons.
2) The number of qualifiers specified below refers to the dominant soil.

For codominant or associated soils, fewer numbers of qualifiers (or even no qualifier) may be
appropriate.
3) Depending on scale, different numbers of principal qualifiers are used:

a. For very small map scales (e.g. smaller than 1:10,000,000), only the
Reference Soil Group (RSG) is used.
b. For next larger map scales (e.g. from 1:5,000,000 to 1:10,000,000), the

RSG plus the first applicable principal qualifier are used.
c. For next larger map scales (e.g. from 1:1,000,000 to 1:5,000,000), the

RSG plus the first two applicable principal qualifiers are used.
d. For next larger map scales (e.g. from 1:250,000 to 1:1,000,000), the RSG plus
the first three applicable principal qualifiers are used.

4) If there are fewer qualifiers applicable than described above, the lesser
number is used.
5) Depending on the purpose of the map or according to national traditions,

at any scale level, further qualifiers may be added optionally. They may be additional
principal qualifiers from further down the list and not already used in the soil name, or they
may be supplementary qualifiers. They are placed using the above-mentioned rules for

supplementary qualifiers. If two or more optional qualifiers are used, the following rules apply:
a. the principal qualifiers are placed first, and of them, the first applicable

qualifier is placed first, and
b. the sequence of any supplementary qualifiers added is decided by the soil
scientist who makes the map.

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