At what level from the sea. Why countries have different “height from sea level”

Not immediately, but then it is nevertheless noticed that the same Mountain peaks on the maps of different countries they have different designations of heights. My friend encountered this paradox three years ago. Sharing his bewilderment, he began to look for the answer to the riddle. At first I assumed that both old and new ones were posted on the Internet. geographic Maps. And since before the height of the mountains was determined not as accurately as today, the designations of heights on the maps of different countries were plus or minus two or three meters. It would seem, what a trifle! But measurements from satellites now give results up to centimeters!

A detailed reconciliation of online maps showed that all of them were digitized in the 90s of the 20th century, and some of them even in the first decade of the current 21st century. In other words, the files are quite fresh and from relatively new original maps. It was also easy to verify the latter: at the bottom of each map there is a date of compilation. The mystery of the inconsistency with the designation of heights for me (not a specialist in cartography) did not lend itself to solution until I paid attention to the words "from the surface of sea level." So, from the level of the world ocean? Somehow I got confused in my reasoning.

The truth was where it should be - in the middle of logical constructions. It was not the tools, not the measurement systems, not the “rounding” of centimeters, etc., but the very concept of absolute height and how it is perceived in different countries.

Absolute altitude any point on the surface of our planet, experts consider the distance from this point to the average level of the surface of the world's oceans. But the whole joke is that in different countries they take the surface “from zero” “in their own way”. For example, in Europe, confusion begins even among landlocked countries. For example, in Switzerland for their maps, zero is taken from the sea surface in Marseille (France). In Austria (also “cut off” from the sea), the surface goes beyond zero Adriatic Sea. The Germans take the level of the sea surface in Amsterdam (Netherlands) as the initial "zero". In Belgium, the reference point is the average level between high and low tide in Ostend. As a result, it turns out that the difference between the height measurements of the Germans and the Belgians exceeds two meters! The examples go on. The question arises by itself: did no one notice the “leapfrog” on maps?

Noticed. And for a very long time. But the whole difficulty lies in the fact that it is extremely costly in terms of finance to bring the measurements to a single reference point for Europe of zero. The problem is not so much that it is difficult, they say, to agree, but that after the adoption of the “single zero”, all geographical maps of Europe would have to be redone, information in documents and reference books would have to be changed. But how, then, with such a significant inconsistency, are they building, for example, bridges on the rivers separating states, as well as railway and automobile tunnels, where accuracy is very important? Specialists first agree on a common measurement system for projects. And only after that they begin to make calculations, carry out drawings, build.

The widely held opinion that the level of the surface of the world's oceans on the planet is the same everywhere, they say, is erroneous. Yes, water is the most plastic substance, and it easily fills any depressions. But due to some features of the terrain, water can not completely fill the recesses to the "edges" everywhere. Satellites have repeatedly recorded “bloatings” of the ocean surface on large area. By the way, astronauts from orbit can clearly see how water with swirls overcomes a narrow strait of Gibraltar and enters the Mediterranean Sea. Basin "A" will never equalize with basin "B" due to the fact that in the Mediterranean Sea the surface level is lower than in the world's oceans. And lower it is due to endless evaporation in the Mediterranean Sea. But when measuring heights, the Swiss "zero" in Marseilles (like the Austrian in the Adriatic inland sea) is from the surface of the sea, and not from the surface of the water near its entrance to the Strait of Gibraltar.

We see a similar incident with “zero” readings on other continents. And there is no mention of a single “standard” yet. Yes, it probably can't be. After all, our planet is not in the form of absolutely round ball, and flattened at the poles and resembles a chicken egg.

From Wikipedia, the free encyclopedia

Height above sea level, absolute height, absolute mark or altitude(lat. Altitudo- height (points of the earth's surface above ocean level)) - one coordinate in three-dimensional geospace (the other two are latitude and longitude), showing at what level, relative to the sea level taken as zero, this or that object is located.

Examples

see also

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Notes

Links

• // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
• - article from the Great Soviet Encyclopedia (3rd edition)

An excerpt characterizing Altitude

sea ​​level

position free surface World app., tending to be perpendicular to the resultant of all forces applied to the mass of water. Changes in the position of surface levels are manifested in fluctuations in sea level.

Sea level

Sea level, the position of the free surface of the water of the seas and oceans, measured along a plumb line relative to the conventional reference point. There are “instantaneous”, tidal, average daily, average monthly, average annual, and average long-term sea levels. Under the influence of wind waves, tides, heating and cooling of the sea surface, fluctuations in atmospheric pressure, precipitation and evaporation, and river and glacial runoff, sea levels change continuously. The long-term mean sea level does not depend on these oscillations of the sea surface. The position of the long-term mean sea level is determined by the distribution of gravity and the spatial unevenness of hydrometeorological characteristics (water density, atmospheric pressure, etc.). The average long-term sea level, constant at each point, is taken as the initial level, from which the heights on land are measured. To measure the depths of seas with low tides, this level is taken as the zero depth - the water level mark, from which the depths are measured in accordance with the requirements of navigation. In the USSR, the absolute heights of points on the earth's surface are counted from the average annual level Baltic Sea, defined from zero footstock in Kronstadt.

Lit .: Duvanin A.I., Sea level, L., 1956; Duvanin A. I., Kalinin G. P., Klige R. K., On long-term fluctuations in the level of the oceans, some seas and lakes, “Bulletin of Moscow State University. Series 5. Geography, 1975, ╧ 6.

Wikipedia

Sea level

Sea level- the position of the free surface of the World Ocean, measured along a plumb line relative to some conventional reference point. This position is determined by the law of gravity, the moment of rotation of the Earth, temperature, tides and other factors. There are "instantaneous", tidal, average daily, average monthly, average annual and average long-term sea levels.

Under the influence of wind waves, tides, heating and cooling of the sea surface, fluctuations in atmospheric pressure, precipitation and evaporation, river and glacial runoff, the sea level is constantly changing. The mean long-term sea level does not depend on these fluctuations of the sea surface. The position of the mean long-term sea level is determined by the distribution of gravity and the spatial unevenness of hydrometeorological characteristics.

The average long-term sea level constant at each point is taken as the initial level, from which heights on land are measured. For reading the depths of seas with low tides, this level is taken as the zero depth - the water level mark, from which the depths are measured in accordance with the requirements of navigation. In Russia and most other countries former USSR, as well as in Poland, the absolute heights of points on the earth's surface are counted from the average annual level of the Baltic Sea, determined from the zero footstock in Kronstadt. Depths and heights in Western European countries are calculated according to the Amsterdam footstock (level measurement mediterranean sea made according to the Marseille footstock).

A tide gauge is used to measure and record sea level fluctuations.

Since there are many factors that affect global weather changes (for example, Global warming), predictions and estimates of ocean level changes in the near future are not particularly accurate.

It was believed that the rise in sea level in the last 20 years has slowed down. However, a new study by surveyors from the University of Tasmania has shown that these calculations are incorrect. A group of scientists led by Christopher Watson published figures in the journal Nature Climate Change, according to which there is really no slowdown - sea levels are rising much faster than previously thought. Previous studies have shown that sea levels have risen by about 3.2 mm per year since 1993, but this figure may actually be an underestimate due to imperfect estimation methods, scientists say.

This means that many geographic locations will be at risk of flooding. "Russian Planet" ranked the most significant places, which can go under water already in this century. Among them - beautiful islands, and big cities: alas, our civilization has developed largely thanks to navigation, and many luxurious megacities are located precisely on the shores of the oceans and seas, at a low altitude above sea level.

1. Maldives

located in warm waters indian ocean islands that many travelers perceive as earthly paradise, have an average height above sea level of 1.5 meters. This means that by about 2100 their population, who lives mainly on the coast, will be forced to leave their homes. The islands are of coral origin, and the depth of the ocean around them is not high: when the atolls disappear under water, they will be visible from the air as vast shoals. Together with the archipelago, its exceptionally rich fauna will also perish.

2. Bangladesh

In this country, floods serve as a political factor: they are usually followed by famine (since water destroys not only people, but also crops), and this leads to crises of confidence in government. This was the case in 1974, when a catastrophic flood that killed 2,000 people and injured 1 million and made several million more homeless forced the government to impose martial law. The largest flood happened relatively recently - in September 1998, due to the flood of the Ganges, Brahmaputra and Meghna, about 300 thousand houses were flooded. Due to rising sea levels, researchers predict the growth of rivers and flooding sea ​​coasts Bangladesh. By the end of the century, half of the country will be at the bottom of a "sea" only one meter deep. Of course, it will be more likely not the sea, but a swamp covered with thickets of trees and shrubs.

Flooding in Bangladesh. Photo: Abir Abdullah / EPA / TASS

3. New Orleans

The birthplace of jazz is below sea level: in different quarters of the city, the figure varies from 1.5 to 3 meters. The city is saved by dams erected after the Flood Control Act was passed in 1965. However, the dams were not as reliable protection as the engineers who built them thought. On August 29, 2005, Hurricane Katrina caused water to breach one of them while waves were able to move over a number of others. As a result, more than 80% of the city area was under water. If the sea level rises, in a few decades the city will become an easy victim for hurricanes, which can be even 1.5-2 times weaker than Katrina.

4. New York

Like New Orleans, this American metropolis has suffered from hurricanes more than once in its history: in 2012, Hurricane Sandy claimed the lives of 185 local residents. Some parts of the city went under water. Eight months after the disaster, Mayor Michael Bloomberg unveiled a plan to protect New York from natural Disasters worth $19.5 billion, one of the main elements of which should be the strengthening coastlines. If a large-scale project is not implemented, by 2080 Long Island and the lower part of the Hudson River Valley may be under water.

5. Bangkok

Bangkok is half empty or half full? According to the most pessimistic expert estimates, part of the Thai capital will go under water already in the 2030s: in addition to rising ocean levels, coastal erosion is working on the death of the city. Save the city could be a giant dam along Gulf of Thailand. But if in the case of New York or New Orleans there is hope for the construction of such giant dams, then the features political situation in the country, most likely, they will not be allowed to carry out a national project to save the city. Now more than a million houses, 90% of which are residential, are at risk, most likely, over time, their first floors will periodically flood.

Consequences heavy rains in Thailand. Photo: Narong Sangnak / EPA / TASS

Another beautiful one american city, famous for its beaches, can become a victim of the waves of the Atlantic. The foundation of the city is formed by limestone rocks that pass water well, which means that the construction of dams, which could help New York, will be completely useless here. It is possible that by the end of the century the city will have to move the inhabitants of some neighborhoods to more high places: the metropolis, as it were, will “creep away” farther and higher from the ocean line.

7. Venice

One of the most romantic cities in the world will disappear into the waves if the level of the world's oceans rises "even" by one meter. In 2008, the city has already suffered from powerful floods: damage to buildings amounted to tens of millions of dollars. As previously noted by experts World Fund wildlife Italy as a whole could lose many of its beaches, resorts and unique coastal flora and fauna. About 60% of Italians live near the sea coasts, and coastal erosion over the past quarter century has led to the disappearance of 42% of the country's beaches.

8. Amsterdam

This city has already been conquered from nature: a third of it is an artificial embankment, which was built over several centuries. The very name of the city, by the way, reflects this fact - it is translated as "Amstel dam", "dam on the river Amstel". Perhaps it is time to pay back to nature: if the water rises by two meters, the city will almost completely go under water. This may happen by the middle of the next century, but even in this century a large part of the city may be at the mercy of the waves.

9. Shanghai

The name of this city literally means "on the sea", and such a location is fraught with a certain danger. Average Height the city above sea level is quite large - 6.5 meters, but there are "lowlands" on its territory, and the number of citizens living in them would be an honor to a large European city- Approximately 5.5 million people. Complicating the situation is the fact that there is almost no flood protection system in the city: the authorities have only recently begun to think about the need for it. In general, Shanghai is far from the only city in China that is threatened by rising sea levels: vast areas of cities such as Guangzhou or Hong Kong are located below sea level.

10. Hamburg

Due to climate change, the city, which is the second largest in Germany, has had to deal with storm surges, rising sea levels and extreme heat in the past few years. Although flood protection systems have a long tradition here - the first dams were built in the Middle Ages, their development may not keep pace with rising sea levels. Now low places the towns adjoining the Elbe are protected by a continuous 14.5 m high dike on both sides of the river. If the climate on the planet continues to change at the same rate as now, this powerful dam may no longer serve as a reliable cover for the city.

Flooding in Hamburg. Photo: Kay Nietfeld / DPA / TASS

How to determine the height of a city above sea level?

The other day I was asked at what height above sea level are Crimean cities Yalta, Alushta and Simferopol. At first I wanted to dismiss this question, but curiosity prompted me to check what the Internet writes on this topic.

It turned out that it is almost impossible to find references to the height of most cities on the web. former Union. Struck by this fact, I decided to correct the situation.

To begin with, I climbed into Wikipedia and made inquiries about what the height above sea level is and from which sea it should be considered. Here is what they write there:

Height above sea level- a coordinate in three-dimensional space (the other two are latitude and longitude), showing at what level, relative to the sea level taken as zero, this or that object is located.

Baltic height system(BSV) - the system adopted in the USSR in 1977 absolute heights, which are counted from zero footstock in Kronstadt. From this mark, the heights of reference geodetic points are counted, which are marked on the ground with various geodetic signs and plotted on maps. At present, the BSV is used in Russia and a number of other CIS countries.

In theory, everything is clear - you need to take a detailed topographic map and see what heights are indicated there. But where did she get this card?

The first thing that came to mind was to look into OziExplorer. This is a special program for working with GPS (satellite navigator). One of its functions allows you to determine the height simply by pointing the cursor at a place on the map. With her help, I easily found out that Alushta is located at altitudes from 0 to 130 meters above sea level. Yalta - from 0 to 200 meters, Sevastopol - from 0 to 100, Simferopol - an average of 250 meters above sea level.

However, this method is not very versatile. After all, the question still remains “where to get a map?”, This time digitized. I had maps of Crimea, but it didn’t work out with the rest of the world ...

The answer literally lay on the surface, that is, on the Internet. It's not the first year that the service has been operating there. Google Earth - a kind of digital globe, glued together from photographs of the earth's surface from a "space" height. There must be a function for determining the height. I downloaded the distribution of Google Earth (free version), installed it and started exploring the menu. There were no altimeters. Strange ... Maybe you need to read the help? Didn't find it either.

Already almost desperate, I suddenly noticed numbers running fast at the bottom of the screen. Eureka! This was the altimeter.

To celebrate, I began to run around the map and measure the height of all the cities in a row.

• The height of Yekaterinburg above sea level is 250 meters.
• The height of Moscow above sea level is 130 meters.
• Saratov - 40
• Makhachkala - 15
• Krasnoyarsk - 140
• Perm — 150
• Chelyabinsk - 250
• Ufa - 125
• Kazan - 90
• Nizhny Novgorod - 70
• Ivanovo - 130
• Yaroslavl - 98
• Voronezh - 104
• Petersburg - 13
• Arkhangelsk - 7
• Novgorod - 28
• Murom - 105

Altitude above sea level of some cities of Ukraine:

• The height of Kyiv above sea level is from 90 (the level of the Dnieper) to 190 (the famous Dnieper steeps) meters.
• Kharkiv - 122
• Chernivtsi - 240
• Khmelnitsky - 299
• Ternopil - 336
• Vinnitsa - 294
• Cherkasy - 80
• Krivoy Rog - 85
• Zaporozhye — 75
• Kherson - 50
• Donetsk - 241
• Dnepropetrovsk - 68
• Sumy — 125
• Poltava - 150
• Chernihiv - 117

In the western part of Ukraine, I was interested in the heights of such settlements:

• Lviv - 270
• Ivano-Frankivsk - 343
• Uzhgorod - 187
• Mukachevo - 181
• Rakhiv - 430
• Yasinya - 650
• Yablonitsky pass - 930

I hope you understand that all the data received is not too accurate. Google Earth is not a professional tool with guaranteed accuracy and reliably known errors. She has very different goals.

In addition, the very term "height of the city above sea level" is very conditional. After all, the city is not a point, but a huge object, different areas which have different heights.