1.
Grade (slope)
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The grade of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of tilt, often slope is calculated as a ratio of rise to run, or as a fraction in which run is the horizontal distance and rise is the vertical distance. The grades or slopes of existing physical features such as canyons and hillsides, stream and river banks, grades are typically specified for new linear constructions. The grade may refer to the slope or the perpendicular cross slope. There are several ways to express slope, as an angle of inclination to the horizontal, as a percentage, the formula for which is 100 rise run which could also be expressed as the tangent of the angle of inclination times 100. In the U. S. this percentage grade is the most commonly used unit for communicating slopes in transportation, surveying, construction, and civil engineering. As a per mille figure, the formula for which is 1000 rise run which could also be expressed as the tangent of the angle of inclination times 1000 and this is commonly used in Europe to denote the incline of a railway. As a ratio of one part rise to so many parts run, for example, a slope that has a rise of 5 feet for every 100 feet of run would have a slope ratio of 1 in 20. This is generally the method used to describe railway grades in Australia, any of these may be used. Grade is usually expressed as a percentage, but this is converted to the angle α from horizontal or the other expressions. Slope may still be expressed when the run is not known. This is not the way to specify slope, it follows the sine function rather than the tangent function. But in practice the way to calculate slope is to measure the distance along the slope and the vertical rise. When the angle of inclination is small, using the slope length rather than the horizontal displacement makes only an insignificant difference, Railway gradients are usually expressed in terms of the rise in relation to the distance along the track as a practical measure. In cases where the difference between sin and tan is significant, the tangent is used. In any case, the identity holds for all inclinations up to 90 degrees, tan α = sin α1 − sin 2 α In Europe. Grades are related using the equations with symbols from the figure at top
2.
Mathematics
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Mathematics is the study of topics such as quantity, structure, space, and change. There is a range of views among mathematicians and philosophers as to the exact scope, Mathematicians seek out patterns and use them to formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proof, when mathematical structures are good models of real phenomena, then mathematical reasoning can provide insight or predictions about nature. Through the use of abstraction and logic, mathematics developed from counting, calculation, measurement, practical mathematics has been a human activity from as far back as written records exist. The research required to solve mathematical problems can take years or even centuries of sustained inquiry, rigorous arguments first appeared in Greek mathematics, most notably in Euclids Elements. Galileo Galilei said, The universe cannot be read until we have learned the language and it is written in mathematical language, and the letters are triangles, circles and other geometrical figures, without which means it is humanly impossible to comprehend a single word. Without these, one is wandering about in a dark labyrinth, carl Friedrich Gauss referred to mathematics as the Queen of the Sciences. Benjamin Peirce called mathematics the science that draws necessary conclusions, David Hilbert said of mathematics, We are not speaking here of arbitrariness in any sense. Mathematics is not like a game whose tasks are determined by arbitrarily stipulated rules, rather, it is a conceptual system possessing internal necessity that can only be so and by no means otherwise. Albert Einstein stated that as far as the laws of mathematics refer to reality, they are not certain, Mathematics is essential in many fields, including natural science, engineering, medicine, finance and the social sciences. Applied mathematics has led to entirely new mathematical disciplines, such as statistics, Mathematicians also engage in pure mathematics, or mathematics for its own sake, without having any application in mind. There is no clear line separating pure and applied mathematics, the history of mathematics can be seen as an ever-increasing series of abstractions. The earliest uses of mathematics were in trading, land measurement, painting and weaving patterns, in Babylonian mathematics elementary arithmetic first appears in the archaeological record. Numeracy pre-dated writing and numeral systems have many and diverse. Between 600 and 300 BC the Ancient Greeks began a study of mathematics in its own right with Greek mathematics. Mathematics has since been extended, and there has been a fruitful interaction between mathematics and science, to the benefit of both. Mathematical discoveries continue to be made today, the overwhelming majority of works in this ocean contain new mathematical theorems and their proofs. The word máthēma is derived from μανθάνω, while the modern Greek equivalent is μαθαίνω, in Greece, the word for mathematics came to have the narrower and more technical meaning mathematical study even in Classical times
3.
Geography
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Geography is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. The first person to use the word γεωγραφία was Eratosthenes, Geography is an all-encompassing discipline that seeks an understanding of the Earth and its human and natural complexities—not merely where objects are, but how they have changed and come to be. It is often defined in terms of the two branches of geography and physical geography. Geography has been called the world discipline and the bridge between the human and the physical sciences, Geography is a systematic study of the Earth and its features. Traditionally, geography has been associated with cartography and place names, although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the space and the temporal database distribution of phenomena, processes, because space and place affect a variety of topics, such as economics, health, climate, plants and animals, geography is highly interdisciplinary. The interdisciplinary nature of the approach depends on an attentiveness to the relationship between physical and human phenomena and its spatial patterns. Names of places. are not geography. know by heart a whole gazetteer full of them would not, in itself and this is a description of the world—that is Geography. In a word Geography is a Science—a thing not of mere names but of argument and reason, of cause, just as all phenomena exist in time and thus have a history, they also exist in space and have a geography. Geography as a discipline can be split broadly into two main fields, human geography and physical geography. The former largely focuses on the environment and how humans create, view, manage. The latter examines the environment, and how organisms, climate, soil, water. The difference between these led to a third field, environmental geography, which combines physical and human geography. Physical geography focuses on geography as an Earth science and it aims to understand the physical problems and the issues of lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns. Physical geography can be divided into broad categories, including, Human geography is a branch of geography that focuses on the study of patterns. It encompasses the human, political, cultural, social, and it requires an understanding of the traditional aspects of physical and human geography, as well as the ways that human societies conceptualize the environment. Integrated geography has emerged as a bridge between the human and the geography, as a result of the increasing specialisation of the two sub-fields. Examples of areas of research in the environmental geography include, emergency management, environmental management, sustainability, geomatics is concerned with the application of computers to the traditional spatial techniques used in cartography and topography
4.
Trigonometric functions
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In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays lie in a plane, but this plane does not have to be a Euclidean plane, Angles are also formed by the intersection of two planes in Euclidean and other spaces. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection. Similar statements hold in space, for example, the angle formed by two great circles on a sphere is the dihedral angle between the planes determined by the great circles. Angle is also used to designate the measure of an angle or of a rotation and this measure is the ratio of the length of a circular arc to its radius. In the case of an angle, the arc is centered at the vertex. In the case of a rotation, the arc is centered at the center of the rotation and delimited by any other point and its image by the rotation. The word angle comes from the Latin word angulus, meaning corner, cognate words are the Greek ἀγκύλος, meaning crooked, curved, both are connected with the Proto-Indo-European root *ank-, meaning to bend or bow. Euclid defines a plane angle as the inclination to each other, in a plane, according to Proclus an angle must be either a quality or a quantity, or a relationship. In mathematical expressions, it is common to use Greek letters to serve as variables standing for the size of some angle, lower case Roman letters are also used, as are upper case Roman letters in the context of polygons. See the figures in this article for examples, in geometric figures, angles may also be identified by the labels attached to the three points that define them. For example, the angle at vertex A enclosed by the rays AB, sometimes, where there is no risk of confusion, the angle may be referred to simply by its vertex. However, in geometrical situations it is obvious from context that the positive angle less than or equal to 180 degrees is meant. Otherwise, a convention may be adopted so that ∠BAC always refers to the angle from B to C. Angles smaller than an angle are called acute angles. An angle equal to 1/4 turn is called a right angle, two lines that form a right angle are said to be normal, orthogonal, or perpendicular. Angles larger than an angle and smaller than a straight angle are called obtuse angles. An angle equal to 1/2 turn is called a straight angle, Angles larger than a straight angle but less than 1 turn are called reflex angles
5.
Inverse trigonometric functions
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In mathematics, the inverse trigonometric functions are the inverse functions of the trigonometric functions. Specifically, they are the inverses of the sine, cosine, tangent, cotangent, secant, and cosecant functions, inverse trigonometric functions are widely used in engineering, navigation, physics, and geometry. There are several notations used for the trigonometric functions. The most common convention is to name inverse trigonometric functions using a prefix, e. g. arcsin, arccos, arctan. This convention is used throughout the article, when measuring in radians, an angle of θ radians will correspond to an arc whose length is rθ, where r is the radius of the circle. Similarly, in programming languages the inverse trigonometric functions are usually called asin, acos. The notations sin−1, cos−1, tan−1, etc, the confusion is somewhat ameliorated by the fact that each of the reciprocal trigonometric functions has its own name—for example, −1 = sec. Nevertheless, certain authors advise against using it for its ambiguity, since none of the six trigonometric functions are one-to-one, they are restricted in order to have inverse functions. There are multiple numbers y such that sin = x, for example, sin =0, when only one value is desired, the function may be restricted to its principal branch. With this restriction, for x in the domain the expression arcsin will evaluate only to a single value. These properties apply to all the trigonometric functions. The principal inverses are listed in the following table, if x is allowed to be a complex number, then the range of y applies only to its real part. Trigonometric functions of trigonometric functions are tabulated below. This is derived from the tangent addition formula tan = tan + tan 1 − tan tan , like the sine and cosine functions, the inverse trigonometric functions can be calculated using power series, as follows. For arcsine, the series can be derived by expanding its derivative,11 − z 2, as a binomial series, the series for arctangent can similarly be derived by expanding its derivative 11 + z 2 in a geometric series and applying the integral definition above. Arcsin = z + z 33 + z 55 + z 77 + ⋯ = ∑ n =0 ∞, for example, arccos x = π /2 − arcsin x, arccsc x = arcsin , and so on. Alternatively, this can be expressed, arctan z = ∑ n =0 ∞22 n 2. There are two cuts, from −i to the point at infinity, going down the imaginary axis and it works best for real numbers running from −1 to 1
6.
Grade separation
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The composition of such transport axes does not have to be uniform, it can consist of a mixture of roads, footpaths, railways, canals, or airport runways. Bridges, tunnels, or a combination of both can be built at a junction to achieve the grade separation. Roads with grade separation generally allow traffic to move freely, with interruptions, and at higher overall speeds. In addition, less trouble between traffic movements reduces the risk of accidents, grade-separated road junctions are typically space-intensive, complicated, and costly, due to the need for large physical structures such as tunnels, ramps, and bridges. Their height can be obtrusive, and this, combined with the traffic volumes that grade-separated roads attract, tend to make them unpopular to nearby landowners. For these reasons, proposals for new grade-separated roads can receive significant public opposition, however, they require significant engineering effort, and are very expensive and time-consuming to construct. Grade-separated pedestrian and cycling routes often require modest space since they do not typically intersect with the facility that they cross, grade-separation can create accessibility problems for people with disabilities due to the vertical gradient required to pass or to reach rail platforms. The term is most widely applied to describe a road junction in which the flow of traffic on one or more of the roads is not disrupted. Instead of a connection, traffic must use on and off ramps or slip roads to access the other roads at the junction. The road which carries on through the junction can also be referred to as grade separated, typically, large freeways, highways, motorways, or dual carriageways are chosen to be grade separated, through their entire length or for part of it. Grade separation drastically increases the capacity of a road compared to a road with at-grade junctions. For instance, it is uncommon to find an at-grade junction on a British motorway, it is all. Interstate Highway, though a few do exist, if traffic can traverse the junction from any direction without being forced to come to a halt, then the junction is described as fully grade separated or free-flowing. These junctions connect two freeways, Stack interchange Cloverleaf interchange These junctions connect two roads, but only one is fully grade-separated, i. e. This situation is most prevalent either where the designer has placed the on-slip to the road before the off-slip at a junction. Weaving can be alleviated by using collector/distributor roads to separate entering and exiting traffic, attempts have been made to increase the capacity of railways by making tracks cross in a grade-separated manner, as opposed to the traditional use of flat crossings to change tracks. A grade-separated rail interchange is known as a junction and one which is not a level junction. Also in Britain, the Southern Railway later made use of flying junctions on other parts of its busy former LSWR main line
7.
Road
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Roads consist of one or two roadways, each with one or more lanes and any associated sidewalks and road verges. Roads that are available for use by the public may be referred to as parkways, avenues, freeways, interstates, highways, or primary, secondary, and tertiary local roads. In urban areas roads may diverge through a city or village and be named as streets, serving a function as urban space easement. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel, historically many roads were simply recognizable routes without any formal construction or maintenance. In the United Kingdom there is ambiguity between the terms highway and road. The Highway code details rules for road users and this includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty, a use tax, is payable on some vehicles used on the public road. The definition of a road depends on the definition of a highway, in the United States, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled. The assertion that the first pathways were the trails made by animals has not been universally accepted, others believe that some roads originated from following animal trails. The Icknield Way is given as an example of type of road origination. By about 10,000 BC, rough roads/pathways were used by human travelers, the worlds oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC. Stone-paved streets are found in the city of Ur in the Middle East dating back to 4000 BC, corduroy roads are found dating to 4000 BC in Glastonbury, England. The Sweet Track, a timber causeway in England, is one of the oldest engineered roads discovered. Built in winter 3807 BC or spring 3806 BC, tree-ring dating enabled very precise dating and it was claimed to be the oldest road in the world until the 2009 discovery of a 6, 000-year-old trackway in Plumstead, London. Brick-paved streets were used in India as early as 3000 BC, in 500 BC, Darius I the Great started an extensive road system for Persia, including the Royal Road, which was one of the finest highways of its time. The road remained in use after Roman times, a hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank. From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, at its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads. In the 8th century AD, many roads were built throughout the Arab Empire, the most sophisticated roads were those in Baghdad, which were paved with tar
8.
Steep grade railway
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A steep grade railway is a railway that ascends and descends a slope that has a steep grade. Such railways can use a number of different technologies to overcome the steepness of the grade, many steep grade railways are located in mountain regions, and are hence also mountain railways. Such railways may form part of infrastructure provided for use by tourists, other steep grade railways are located in hilly urban areas. Again these may be largely tourist oriented, or may be used as part of the public transport provision. On steep grades the friction between the wheels and the rails cannot apply sufficient adhesion to the wheels so as to overcome gravity. Where the line is too steep to rely on adhesion for climbing, a now little used alternative to the rack and pinion railway is the Fell system, in which traction and/or braking wheel are applied to a central rail under pressure. Another alternative is a car in which the car runs on rails. This is used in San Franciscos famous cable cars, finally at the steepest end of the spectrum, a funicular railway may be used. Here a cable is used to haul counterbalanced trains up and down the track, the cars are permanently attached to the cable, which stops, starts and reverses as required. Cars are often built for the slope, with specially raked seating. Taken to its conclusion as the slope becomes vertical, a funicular becomes an elevator. List of steepest gradients on adhesion railways List of Fell system railways List of cog and rack railways List of cable hauled railways List of funicular railways Hillclimbing
9.
Rack railway
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A rack railway is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with this rack rail and this allows the trains to operate on steep grades above around 7 to 10%, which is the maximum for friction-based rail. Most rack railways are mountain railways, although a few are transit railways or tramways built to overcome a steep gradient in an urban environment. The first cog railway was the Middleton Railway between Middleton and Leeds in West Yorkshire, England, UK, where the first commercially successful steam locomotive, Salamanca and this used a rack and pinion system designed and patented in 1811 by John Blenkinsop. The first mountain cog railway was the Mount Washington Cog Railway in the US state of New Hampshire, the track was completed to reach the summit of Mount Washington in 1869. The first mountain railway in continental Europe was the Vitznau-Rigi-Bahn on Mount Rigi in Switzerland. A number of different rack systems have been developed, today, the majority of rack railways use the Abt system. Blenkinsops system remained in use for 25 years on the Middleton Railway, Rack systems place the rack rail halfway between the running rails, with the exception of some early Morgan rack installations. The first successful rack railway in the US was the Mount Washington Cog Railway, the first public trial of the Marsh rack on Mount Washington was made on August 29,1866, when only one quarter of a mile of track had been completed. The Mount Washington railway opened to the public on August 14,1868, the Riggenbach rack system was invented by Niklaus Riggenbach working at about the same time as, but independently from Marsh. Riggenbach was granted a French patent in 1863 based on a model which he used to interest potential Swiss backers. During this time, the Swiss Consul to the United States visited Marshs Mount Washington Cog Railway, eager to boost tourism in Switzerland, the government commissioned Riggenbach to build a rack railway up Rigi Mountain. Following the construction of a locomotive and test track in a quarry near Bern. The Riggenbach system is similar in design to the Marsh system and it uses a ladder rack, formed of steel plates or channels connected by round or square rods at regular intervals. The Riggenbach system suffers from the problem that its fixed ladder rack is more complex, following the success of the Vitznau-Rigi-Bahn, Riggenbach established the Maschinenfabrik der Internationalen Gesellschaft für Bergbahnen - a company that produced rack locomotives to his design. The Strub rack system was invented by Emil Strub in 1896 and it uses a rolled flat-bottom rail with rack teeth machined into the head approximately 100 mm apart. Safety jaws fitted to the locomotive engage with the underside of the head to prevent derailments, strubs US Patent, granted in 1898, also includes details of how the rack rail is integrated with the mechanism of a turnout. The best-known use of the Strub system is on the Jungfraubahn in Switzerland and it is the simplest rack system to maintain and has become increasingly popular
10.
Netherlands
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The Netherlands, also informally known as Holland is the main constituent country of the Kingdom of the Netherlands. It is a densely populated country located in Western Europe with three territories in the Caribbean. The European part of the Netherlands borders Germany to the east, Belgium to the south, and the North Sea to the northwest, sharing borders with Belgium, the United Kingdom. The three largest cities in the Netherlands are Amsterdam, Rotterdam and The Hague, Amsterdam is the countrys capital, while The Hague holds the Dutch seat of parliament and government. The port of Rotterdam is the worlds largest port outside East-Asia, the name Holland is used informally to refer to the whole of the country of the Netherlands. Netherlands literally means lower countries, influenced by its low land and flat geography, most of the areas below sea level are artificial. Since the late 16th century, large areas have been reclaimed from the sea and lakes, with a population density of 412 people per km2 –507 if water is excluded – the Netherlands is classified as a very densely populated country. Only Bangladesh, South Korea, and Taiwan have both a population and higher population density. Nevertheless, the Netherlands is the worlds second-largest exporter of food and agricultural products and this is partly due to the fertility of the soil and the mild climate. In 2001, it became the worlds first country to legalise same-sex marriage, the Netherlands is a founding member of the EU, Eurozone, G-10, NATO, OECD and WTO, as well as being a part of the Schengen Area and the trilateral Benelux Union. The first four are situated in The Hague, as is the EUs criminal intelligence agency Europol and this has led to the city being dubbed the worlds legal capital. The country also ranks second highest in the worlds 2016 Press Freedom Index, the Netherlands has a market-based mixed economy, ranking 17th of 177 countries according to the Index of Economic Freedom. It had the thirteenth-highest per capita income in the world in 2013 according to the International Monetary Fund, in 2013, the United Nations World Happiness Report ranked the Netherlands as the seventh-happiest country in the world, reflecting its high quality of life. The Netherlands also ranks joint second highest in the Inequality-adjusted Human Development Index, the region called Low Countries and the country of the Netherlands have the same toponymy. Place names with Neder, Nieder, Nether and Nedre and Bas or Inferior are in use in all over Europe. They are sometimes used in a relation to a higher ground that consecutively is indicated as Upper, Boven, Oben. In the case of the Low Countries / the Netherlands the geographical location of the region has been more or less downstream. The geographical location of the region, however, changed over time tremendously
11.
Poland
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Poland, officially the Republic of Poland, is a country in Central Europe, situated between the Baltic Sea in the north and two mountain ranges in the south. Bordered by Germany to the west, the Czech Republic and Slovakia to the south, Ukraine and Belarus to the east, the total area of Poland is 312,679 square kilometres, making it the 69th largest country in the world and the 9th largest in Europe. With a population of over 38.5 million people, Poland is the 34th most populous country in the world, the 8th most populous country in Europe, Poland is a unitary state divided into 16 administrative subdivisions, and its capital and largest city is Warsaw. Other metropolises include Kraków, Wrocław, Poznań, Gdańsk and Szczecin, the establishment of a Polish state can be traced back to 966, when Mieszko I, ruler of a territory roughly coextensive with that of present-day Poland, converted to Christianity. The Kingdom of Poland was founded in 1025, and in 1569 it cemented a political association with the Grand Duchy of Lithuania by signing the Union of Lublin. This union formed the Polish–Lithuanian Commonwealth, one of the largest and most populous countries of 16th and 17th century Europe, Poland regained its independence in 1918 at the end of World War I, reconstituting much of its historical territory as the Second Polish Republic. In September 1939, World War II started with the invasion of Poland by Nazi Germany, followed thereafter by invasion by the Soviet Union. More than six million Polish citizens died in the war, after the war, Polands borders were shifted westwards under the terms of the Potsdam Conference. With the backing of the Soviet Union, a communist puppet government was formed, and after a referendum in 1946. During the Revolutions of 1989 Polands Communist government was overthrown and Poland adopted a new constitution establishing itself as a democracy, informally called the Third Polish Republic. Since the early 1990s, when the transition to a primarily market-based economy began, Poland has achieved a high ranking on the Human Development Index. Poland is a country, which was categorised by the World Bank as having a high-income economy. Furthermore, it is visited by approximately 16 million tourists every year, Poland is the eighth largest economy in the European Union and was the 6th fastest growing economy on the continent between 2010 and 2015. According to the Global Peace Index for 2014, Poland is ranked 19th in the list of the safest countries in the world to live in. The origin of the name Poland derives from a West Slavic tribe of Polans that inhabited the Warta River basin of the historic Greater Poland region in the 8th century, the origin of the name Polanie itself derives from the western Slavic word pole. In some foreign languages such as Hungarian, Lithuanian, Persian and Turkish the exonym for Poland is Lechites, historians have postulated that throughout Late Antiquity, many distinct ethnic groups populated the regions of what is now Poland. The most famous archaeological find from the prehistory and protohistory of Poland is the Biskupin fortified settlement, dating from the Lusatian culture of the early Iron Age, the Slavic groups who would form Poland migrated to these areas in the second half of the 5th century AD. With the Baptism of Poland the Polish rulers accepted Christianity and the authority of the Roman Church
12.
Czech Republic
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The Czech Republic, also known as Czechia, is a nation state in Central Europe bordered by Germany to the west, Austria to the south, Slovakia to the east and Poland to the northeast. The Czech Republic covers an area of 78,866 square kilometres with mostly temperate continental climate and it is a unitary parliamentary republic, has 10.5 million inhabitants and the capital and largest city is Prague, with over 1.2 million residents. The Czech Republic includes the territories of Bohemia, Moravia. The Czech state was formed in the late 9th century as the Duchy of Bohemia under the Great Moravian Empire, after the fall of the Empire in 907, the centre of power transferred from Moravia to Bohemia under the Přemyslid dynasty. In 1002, the duchy was formally recognized as part of the Holy Roman Empire, becoming the Kingdom of Bohemia in 1198 and reaching its greatest territorial extent in the 14th century. Following the Battle of Mohács in 1526, the whole Crown of Bohemia was gradually integrated into the Habsburg Monarchy alongside the Archduchy of Austria, the Protestant Bohemian Revolt against the Catholic Habsburgs led to the Thirty Years War. After the Battle of the White Mountain, the Habsburgs consolidated their rule, reimposed Roman Catholicism, the Czech part of Czechoslovakia was occupied by Germany in World War II, and was liberated in 1945 by the armies of the Soviet Union and the United States. The Czech country lost the majority of its German-speaking inhabitants after they were expelled following the war, the Communist Party of Czechoslovakia won the 1946 elections. Following the 1948 coup détat, Czechoslovakia became a one-party communist state under Soviet influence, in 1968, increasing dissatisfaction with the regime culminated in a reform movement known as the Prague Spring, which ended in a Soviet-led invasion. Czechoslovakia remained occupied until the 1989 Velvet Revolution, when the communist regime collapsed, on 6 March 1990, the Czech Socialistic Republic was renamed to the Czech Republic. On 1 January 1993, Czechoslovakia peacefully dissolved, with its constituent states becoming the independent states of the Czech Republic and the Slovak Republic. The Czech Republic joined NATO in 1999 and the European Union in 2004, it is a member of the United Nations, the OECD, the OSCE, and it is a developed country with an advanced, high income economy and high living standards. The UNDP ranks the country 14th in inequality-adjusted human development, the Czech Republic also ranks as the 6th most peaceful country, while achieving strong performance in democratic governance. It has the lowest unemployment rate in the European Union, the traditional English name Bohemia derives from Latin Boiohaemum, which means home of the Boii. The current name comes from the endonym Čech, spelled Cžech until the reform in 1842. The name comes from the Slavic tribe and, according to legend, their leader Čech, the etymology of the word Čech can be traced back to the Proto-Slavic root *čel-, meaning member of the people, kinsman, thus making it cognate to the Czech word člověk. The country has traditionally divided into three lands, namely Bohemia in the west, Moravia in the southeast, and Czech Silesia in the northeast. Following the dissolution of Czechoslovakia at the end of 1992, the Czech part of the former nation found itself without a common single-word geographical name in English, the name Czechia /ˈtʃɛkiə/ was recommended by the Czech Ministry of Foreign Affairs
