Definition of terms

Terms about demography

Age dependency ratio
The ratio of persons in "dependent" ages (generally under age 15 and over age 64) to those in "economically productive" ages (15 to 64 years) in the population. It is sometimes divided into the old-age dependency (the ratio of people aged 65 and older to those aged 15 to 64 years), and the child dependency (ratio of people under 15 to those aged 15 to 64 years). (Source: Philippine Statistics Authority)
Median age
The age that divides a population into two numerically equal groups, that is, half of the population are younger than this age, and the other half are older. (Source: Philippine Statistics Authority)
Population growth rate
The rate at which the population increases within a given time or period. Applies/refers to the calculated growth rates between each census.

Terms about distance

Great-circle distance
The shortest distance between two points along the surface of a sphere or ellipsoid. Applies/refers to the shortest distance between two cities or towns (using the city/municipal center coordinates as points).

Terms about rivers

Headwaters
The place where a river begins is called its source. River sources are also called headwaters. (Source: National Geographic Society. "Source." National Geographic, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/source/.)
River basin
A river drainage basin is an area drained by a river and all of its tributaries. A river basin is made up of many different watersheds. (Source: National Geographic Society. "Basin." National Geographic, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/basin/.)
River mouth
The place where a river enters a lake, larger river, or the ocean. (Source: National Geographic Society. "Mouth." National Geographic, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/mouth/.)
Tributary
A freshwater stream that feeds into a larger stream, river or other body of water. (Source: National Geographic Society. "Tributary." National Geographic, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/tributary/.)
Watershed
A watershed is an entire river system — an area drained by a river and its tributaries. It is sometimes called a drainage basin. (Source: National Geographic Society. "Watershed." National Geographic, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/watershed/.)

Terms about roads

Primary Road
National Road classification, a road that connects major cities with population of at least 100,000. (Source: Department of Public Works and Highways)
Secondary Road
National Road classification, a road which complements the national primary roads to provide access to main population and production centers of the country. (Source: Department of Public Works and Highways)
Tertiary Road
National Road classification, an existing road under the DPWH which performs a local function. (Source: Department of Public Works and Highways)

Terms about volcanoes

Active
Erupted within historical times (within the last 600 years). (Source: Philippine Institute of Volcanology and Seismology)
Potentially active
Morphologically young-looking but with no historical or analytical records of eruptions. (Source: Philippine Institute of Volcanology and Seismology)
Inactive
No recorded eruptions; physical form has been intensively weathered and eroded, bearing deep and long gullies. (Source: Philippine Institute of Volcanology and Seismology)
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