Perimeter in the context of "Physical dimension"

In geometry, the area enclosed by a circle of radius r is πr. Here, the Greek letter π represents the constant ratio of the circumference of any circle to its diameter, approximately equal to 3.14159.

One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons with an increasing number of sides. The area of a regular polygon is half its perimeter multiplied by the distance from its center to its sides, and because the sequence tends to a circle, the corresponding formula–that the area is half the circumference times the radius–namely, A = ⁠1/2⁠ × 2πr × r, holds for a circle.

In Euclidean geometry, a regular polygon is a polygon that is direct equiangular (all angles are equal in measure) and equilateral (all sides have the same length). Regular polygons may be either convex or star. In the limit, a sequence of regular polygons with an increasing number of sides approximates a circle, if the perimeter or area is fixed, or a regular apeirogon (effectively a straight line), if the edge length is fixed.

Antigua (/ænˈtiːɡə/ ann-TEE-gə; Antiguan Creole: Aanteega), also known as Waladli or Wadadli by the local population, is an island in the Lesser Antilles. It is one of the Leeward Islands in the Caribbean region and the most populous island of the country of Antigua and Barbuda. Antigua and Barbuda became an independent state within the Commonwealth of Nations on 1 November 1981.

The island's perimeter is roughly 87 km (54 mi) and its area 281 km (108 sq mi). Its population was 83,191 (at the 2011 Census). The economy is mainly reliant on tourism, with the agricultural sector serving the domestic market.

Size in general is the magnitude or dimensions of a thing. More specifically, geometrical size (or spatial size) can refer to three geometrical measures: length, area, or volume. Length can be generalized to other linear dimensions (width, height, diameter, perimeter). Size can also be measured in terms of mass, especially when assuming a density range.

In mathematical terms, "size is a concept abstracted from the process of measuring by comparing a longer to a shorter". Size is determined by the process of comparing or measuring objects, which results in the determination of the magnitude of a quantity, such as length or mass, relative to a unit of measurement. Such a magnitude is usually expressed as a numerical value of units on a previously established spatial scale, such as meters or inches.

The coastline paradox is the counterintuitive observation that the coastline of a landmass does not have a well-defined length or perimeter. This results from the fractal curve–like properties of coastlines; i.e., the fact that a coastline typically has a fractal dimension. Although the "paradox of length" was previously noted by Hugo Steinhaus, the first systematic study of this phenomenon was by Lewis Fry Richardson, and it was expanded upon by Benoit Mandelbrot.

The measured length of the coastline depends on the method used to measure it and the degree of cartographic generalization. Since a landmass has features at all scales, from hundreds of kilometers in size to tiny fractions of a millimeter and below, there is no obvious size of the smallest feature that should be taken into consideration when measuring, and hence no single well-defined perimeter to the landmass. Various approximations exist when specific assumptions are made about minimum feature size.

In ancient Greek and Roman architecture, a peristyle (/ˈpɛrɪˌstaɪl/; Ancient Greek: περίστυλον, romanized: perístulon) is a continuous porch formed by a row of columns (a colonnade) surrounding the perimeter of a building or a courtyard. Tetrastoön (τετράστῳον/τετράστοον, tetrástōion/tetrástoon, 'four arcades') is a rarely used archaic term for this feature. The peristyle in a Greek temple is a peristasis (περίστασις, perístasis). In the Christian ecclesiastical architecture that developed from the Roman basilica, a courtyard peristyle and its garden came to be known as a cloister.

In classical geometry, a radius (pl.: radii or radiuses) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is the line segment or distance from its center to any of its vertices. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel. The typical abbreviation and mathematical symbol for radius is R or r. By extension, the diameter D is defined as twice the radius:

If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere. In either case, the radius may be more than half the diameter, which is usually defined as the maximum distance between any two points of the figure. The inradius of a geometric figure is usually the radius of the largest circle or sphere contained in it. The inner radius of a ring, tube or other hollow object is the radius of its cavity.