## Boundary problem (spatial analysis)

A boundary problem in analysis is a phenomenon in which geographical patterns are differentiated by the shape and arrangement of boundaries that are drawn for administrative or measurement purposes. The boundary problem occurs because of the loss of neighbors in analyses that depend on the values of the neighbors. While geographic phenomena are measured and analyzed within a specific unit, identical spatial data can appear either dispersed or clustered depending on the boundary placed around the data. In analysis with point data, dispersion is evaluated as dependent of the boundary. In analysis with areal data, statistics should be interpreted based upon the boundary.

## Degua Tembien

Dogua Tembien is one of the woredas in the Tigray Region of Ethiopia. It is named in part after the former province of Tembien. Nowadays, the mountainous district is part of the Southeastern Tigray Zone. The administrative centre of this woreda is Hagere Selam.

## Distance decay

Distance decay is a geographical term which describes the effect of distance on cultural or spatial interactions. The distance decay effect states that the interaction between two locales declines as the distance between them increases. Once the distance is outside of the two locales activity space, their interactions begin to decrease. With the advent of faster travel, distance has less effect than it did in the past, except where places previously connected by now-abandoned railways, for example, have fallen off the beaten path. Advances in communications technology, such as telegraphs, telephones, broadcasting, and internet, have further decreased the effects of distance. Distance decay is graphically represented by a curving line that swoops concavely downward as distance along the x-axis increases. Distance decay can be mathematically represented as an Inverse-square law by the expression I = c o n s t. × d − 2 {\displaystyle I=const.\times d^{-2}} or I ∝ 1 / d 2 {\displaystyle I\propto 1/d^{2}}, where I is interaction and d is distance. It can take other forms such as negative exponential, i.e. I ∝ e − d {\displaystyle I\propto e^{-d}}. Distance decay is evident in town/city centres. It can refer to various things which decline with greater distance from the center of the Central Business District CBD: price of land street quality quality of shops depending on definitions of quality and center height of buildings density of pedestrian traffic Distance decay weighs into the decision to migrate, leading many migrants to move less far.

## Earth section paths

Earth section paths are paths on the earth defined by the intersection of a reference ellipsoid and a plane. Common examples of earth sections include the great ellipse and normal sections. This page provides a unifying approach to all earth sections and their associated geodetic problems.

## Easting and northing

Easting and northing are geographic Cartesian coordinates for a point. Easting is the eastward-measured distance and northing is the northward-measured distance. When using common projections such as the transverse Mercator projection, these are distances projected on an imaginary surface similar to a bent sheet of paper, and are not the same as distances measured on the curved surface of the Earth. Easting and northing coordinates are commonly measured in metres from the axes of some horizontal datum. However, other units e.g., survey feet are also used. The coordinates are most commonly associated with the Universal Transverse Mercator coordinate system UTM, which has unique zones that cover the Earth to provide detailed referencing.

## Economic restructuring

Economic restructuring is used to indicate changes in the constituent parts of an economy in a very general sense. In the western world, it is usually used to refer to the phenomenon of urban areas shifting from a manufacturing to a service sector economic base. It has profound implications for productive capacities and competitiveness of cities and regions. This transformation has affected demographics including income distribution, employment, and social hierarchy; institutional arrangements including the growth of the corporate complex, specialized producer services, capital mobility, informal economy, nonstandard work, and public outlays; as well as geographic spacing including the rise of world cities, spatial mismatch, and metropolitan growth differentials.

## Edaga Arbi Glacials

The Edaga Arbi Glacials are a Palaeozoic geological formation in Tigray and in Eritrea. The matrix is composed of grey, black and purple clays, that contains rock fragments up to 6 metres across. Pollen dating yields a Late Carboniferous to Early Permian age.

## Edgelands

Edgelands are the transitional, liminal areas of space to be found on the boundaries of country and town - with the spread of urbanisation, an increasingly important facet of the twenty-first century world.

## Enticho Sandstone

The Enticho Sandstone is a geological formation in north Ethiopia. It forms the lowermost sedimentary rock formation in the region and lies directly on the basement rocks. Enticho Sandstone consists of arenite that is rich in quartz. The formation has a maximum thickness of 200 metres. Locally, its upper part is coeval with the Edaga Arbi Glacials. The Enticho Sandstone has been deposited during the Ordovician, as evidenced by impressions of organisms.

## Extreme environment

An extreme environment is a habitat that is considered very hard to survive in due to its considerably extreme conditions such as temperature, accessibility to different energy sources or under high pressure. For an area to be considered an extreme environment, it must contain certain conditions and aspects that are considered very hard for other life forms to survive. Pressure conditions may be extremely high or low; high or low content of oxygen or carbon dioxide in the atmosphere; high levels of radiation, acidity, or alkalinity; absence of water; water containing a high concentration of salt or sugar; the presence of sulphur, petroleum, and other toxic substances. Examples of extreme environments include the geographical poles, very arid deserts, volcanoes, deep ocean trenches, upper atmosphere, Mt Everest, outer space, and the environments of every planet in the Solar System except the Earth. Any organisms living in these conditions are often very well adapted to their living circumstances, which is usually a result of long-term evolution. Physiologists have long known that organisms living in extreme environments are especially likely to exhibit clear examples of evolutionary adaptation because of the presumably intense past natural selection they have experienced.

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