Cartography Flashcards
Explain the International Date Line and Time Zones.
• The International Date Line (IDL) is an imaginary line on the surface of the Earth that runs from the north to the south pole and demarcates the change of one calendar day to the next.
It passes through the middle of the Pacific Ocean, roughly following the 180° longitude but deviating to pass around some territories and island groups.
• The IDL zigzags around the antimeridian, which is on the opposite side of the Earth to the Prime Meridian.
• The Prime Meridian is used to define Universal Time and is the meridian from which all other time zones are calculated.
Time zones to the east of the Prime Meridian are in advance of Coordinated Universal Time (UTC) (up to UTC+14); time zones to the west are behind UTC (to UTC-12).
The IDL is the line between those highest (up to UTC+14) and those lowest (down to UTC−12) time zones.
• The IDL and the moving point of midnight separate the two calendar days that are current somewhere on Earth.
* **However, during a two-hour period between 10:00 and 11:59 (UTC) each day, three different calendar days are in use. (This is because of daylight saving in the UTC+12 zone and the use of additional date-shifted time zones in areas east of the 180th meridian) * **These additional time zones result in the standard time and date in some communities being 24 or 25 hours different from the standard time and date in others.
• A traveler crossing the IDL eastbound subtracts one day, or 24 hours, so that the calendar date to the west of the line is repeated after the following midnight. Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day.
The IDL is necessary to have a fixed, albeit arbitrary, boundary on the globe where the calendar date advances in the westbound direction.
• For parts of its length, the IDL follows the meridian of 180° longitude, roughly down the middle of the Pacific Ocean.
To avoid crossing nations internally, the IDL deviates west around the US Aleutian Islands, separating them from islands in the far east of Russia, and further south, it deviates east around various island nations in the Pacific such as Kiribati, Samoa, Tonga and Tokelau.
These various deviations, east or west, generally accommodate the political and/or economic affiliations of the affected areas.
Short note on Indian Standard Time.
- Indian Standard Time (IST) is the time observed throughout India and Sri Lanka, with a time offset of UTC+05:30.
- India does not observe Daylight Saving Time (DST) or other seasonal adjustments.
- In military and aviation time IST is designated E* (“Echo-Star”).
- IST is calculated on the basis of 82.5° E longitude, in Shankargarh Fort, Mirzapur (25.15°N 82.58°E) (in Allahabad district in the state of Uttar Pradesh) which is nearly on the corresponding longitude reference line.
- In the tz database it is represented by Asia/Kolkata.
Explain Geographic Coordinate System. Along with definitions of: Latitude, Longitude, Equator, Prime-Meridian, and Graticule.
A geographic coordinate system is a coordinate system that enables every location on the Earth to be specified by a set of numbers or letters.
The coordinates are often chosen such that one of the numbers represents vertical position, and two or three of the numbers represent horizontal position.
A common choice of coordinates is latitude, longitude and elevation.
Latitude:
• Are the (imaginary) parallel/horizontal lines running along the surface of the globe, slicing the globe in horizontal plates.
• The “latitude” (abbreviation: Lat., φ, or phi) of a point on the Earth’s surface is the angle between the equatorial plane and the straight line that passes through that point and through (or close to) the center of the Earth.
Lines joining points of the same latitude trace circles on the surface of the Earth called parallels, as they are parallel to the equator and to each other.
The north pole is 90° N; the south pole is 90° S. The 0° parallel of latitude is designated the equator, the fundamental plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres.
longitude:
• (abbreviation: Long., λ, or lambda) of a point on the Earth’s surface is the angle east or west from a reference meridian to another meridian that passes through that point.
• All meridians are halves of great ellipses (often improperly called great circles), which converge at the north and south poles. The meridian of the British Royal Observatory in Greenwich, a little east of London, England, is the international Prime Meridian although some organizations—such as the French Institut Géographique National—continue to use other meridians for internal purposes.
The Prime Meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side.
The antipodal meridian of Greenwich is both 180°W and 180°E. ***This is not to be conflated with the International Date Line, which diverges from it in several places for political reasons including between far eastern Russia and the far western Aleutian Islands.
• The combination of these two components specifies the position of any location on the surface of the Earth, without consideration of altitude or depth. The grid thus formed by latitude and longitude is known as the “GRATICULE”.
The zero/zero point of this system is located in the Gulf of Guinea about 625 km (390 mi) south of Tema, Ghana.
What is Standard Time? and how is it measured?
- Standard Time is the time kept on land.
- Countries may adopt a uniform or multiple time zones keeping in mind the extent of its boundaries longitudinally.
- Many countries also vary their time seasonally on account of the varying amount of daylight throughout the year. Such seasonal changes are called ‘Daylight Saving Time’
- Standard Time is measured in relation to the zero time zone/Greenwich Mean Time (GMT)/Universal Time (UT)
Explain Daylighting Saving Time with its rationale and its relevance to Indian context with reference to Assam’s intent to switch to ‘Chaibagan/Bagan Time’ debate.
> Daylight saving time (DST) or summer time is the practice of advancing clocks during summer months by one hour so that in the evening hours day light is experienced later, while sacrificing normal sunrise times.
• Typically, users in regions with summer time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time.
• New Zealander George Hudson proposed the modern idea of daylight saving in 1895. Germany and Austria-Hungary organized the first implementation, starting on 30 April 1916. Many countries have used it at various times since then, particularly since the energy crisis of the 1970s.
> The practice has received both advocacy and criticism:
• Putting clocks forward BENEFITS RETAILING, SPORTS and other activities that exploit sunlight after working hours, but can cause PROBLEMS FOR EVENING ENTERTAINMENT and for other activities tied to sunlight, such as FARMING.
• Although some early proponents of DST aimed to reduce evening use of incandescent lighting, which was formerly a primary use of electricity, modern heating and cooling usage patterns differ greatly and research about how DST CURRENTLY AFFECTS ENEGY USE IS LIMITED or CONTRADICTORY.
> DST clock shifts sometimes COMPLICATES TIMEKEEPING and can disrupt travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns. Computer software can often adjust clocks automatically, but policy changes by various jurisdictions of the dates and timings of DST may be confusing.
Rationale:
> Industrialized societies generally follow a clock-based schedule for daily activities that does not change throughout the course of the year.
The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society’s daily routines for work and personal conduct are more likely governed by the length of daylight hours and solar time, which change seasonally because of the Earth’s axial tilt.
• North and south of the tropics daylight lasts longer in summer and shorter in winter, the effect becoming greater as one moves away from the tropics.
> By synchronously resetting all clocks in a region to one hour ahead of Standard Time (one hour “fast”), individuals who follow such a year-round schedule will wake an hour earlier than they would have otherwise; they will begin and complete daily work routines an hour earlier, and they will have an extra hour of daylight after their workday activities.
• However, they will have one less hour of daylight at the start of each day, making the policy less practical during winter. While the times of sunrise and sunset change at roughly equal rates as the seasons change, proponents of Daylight Saving Time argue that most people prefer a greater increase in daylight hours after the typical “nine-to-five” workday.
• Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed.
• The manipulation of time at higher latitudes (for example Iceland, Nunavut or Alaska) has little impact on daily life, because the length of day and night changes more extremely throughout the seasons (in comparison to other latitudes), and thus sunrise and sunset times are significantly out of sync with standard working hours regardless of manipulations of the clock.
> > DST is also of little use for locations near the equator, because these regions see only a small variation in daylight throughout the year.
Assam’s Chaibagan Time debate:
> In January 2014, administration of the Indian state of Assam has just decided to break away from India Standard Time (IST).
• If the central government of India does not stop the move, clocks there will be set forward permanently. It is not yet known when the switch will occur.
Why return to “bagaan time”?
> The time zone change comes 150 years after the British colonialists introduced “chaibagaan time” or “bagaan time”, a time schedule observed by tea planters, which too was 1Hr AHEAD of IST. Assam, along with the rest of India, has been following IST for the past 66 years.
> “IST has affected our productivity besides forcing us to follow a schedule not suited to the time zone we are in”, the Hindustan Times quotes Assam chief minister, Tarun Gogoi. “We have now decided to set our clocks to bagaan time.”
> While IST is calculated on the basis of solar time in Allahabad in the northern-central state of Uttar Pradesh, Assam lies in the extreme east of the country and borders Bangladesh and Buthan. This means that the sun sets as early as 16:31 (4:31 p.m.) IST in November and December.
Time in India
> Clocks in India are 5:30 hours ahead of Coordinated Universal Time (UTC), making the country one of the few territories with a half-hour UTC offset. If the time zone change is implemented, Assam will be 6:30 hours ahead of UTC. India does not observe daylight saving time (DST).
Ramifications for other states:
Assam is surrounded by and shares its unique geographic location in the far eastern corner of India with the states of Arunachal Pradesh, Meghalaya, Manipur, Mizoram, Nagaland, and Tripura. It is not yet known if these states will follow Assam’s time zone switch.
Which country in the world fall on all the 4-hemispheres?
Kiribati an archipelago nation of Oceania continent and part of Micronesia
Where is Tropic of Cancer? How many/which countries does it pass through?
Tropic of Cancer is at 23.5*N. It passes through following (considering all identified and disputed/controversial countries and territorial sea) 19 countries [if we take into account one territorial waters/archipelago (Hawaii), one disputed territory as sovereign country (Western Sahara), and one contentious political/legal claim (Taiwan) as valid]:
- USA^ (Through Hawaiian Islands -territorial waters- in Pacific Ocean)
- Mexico
- The Bahamas
- Western Sahara^ [Disputed territory: Identified as ‘Non-self-governing territory’ by UN since 1963; Morocco (2/3 of the country including most of the Atlantic coast) and SADR (Sahrawi Arab Democratic Republic) Govt in exile in Algeria]
- Mauritania
- Mali
- Algeria
- Niger
- Libya
- Chad
- Egypt
- Saudi Arabia
- UAE
- Oman
- India
- Bangladesh
- Myanmar
- China
- Taiwan/Republic of China/Chinese Taipei^ [Political and legal status is contentious but most of the international community recognises China’s claim on Taiwan]
Through how many/which countries does Equator pass through?
Equator passes through 14 countries:
- Kiribati
- USA (Baker Is, through territorial waters/sea)
- Ecuador
- Colombia
- Brazil
- São Tomé and Principe
- Gabon
- Congo
- D R Congo
- Uganda
- Kenya
- Somalia
- Maldives
- Indonesia
Where is Tropic of Capricorn? How many countries does it pass through?
Tropic of Capricorn is at 23.5*S and passes through 11 countries:
- Australia
- France (French Polynesia)
- Chile
- Argentina
- Paraguay
- Brazil
- Namibia
- Botswana
- South Africa
- Mozambique
- Madagascar
What is Prime Meridian and IERS Reference Meridian? Through how many countries does it pass? Which PM did India used 4th century CE?
Prime Meridian:
• A prime meridian is a meridian (a line of longitude) in a geographical coordinate system at which longitude is defined to be 0°.
• A prime meridian and its opposite in a 360°-system, the 180th meridian (at 180° longitude), form a great circle.
This great circle divides the sphere, e.g., the Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called Eastern Hemisphere and Western Hemisphere.
• A prime meridian is ultimately arbitrary, unlike an equator, which is determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history.
International prime meridian / Meridian of Greenwich :
In October 1884 the Greenwich Meridian was selected by delegates (forty-one delegates representing twenty-five nations) to the International Meridian Conference held in Washington, D.C., United States to be the common zero of longitude and standard of time reckoning throughout the world.
The modern prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy in 1851.
IERS (International Earth Rotation and Reference System) Reference Meridian:
• Satellites changed the reference from the surface of the Earth to its center of mass around which all satellites orbit regardless of surface irregularities.
The first satellite navigation system, TRANSIT, selected in the 1960s as its reference meridian on an Earth-centered ellipsoid the longitude on the NAD27 ellipsoid of its development laboratory halfway between Washington, D.C. and Baltimore, Maryland.
These identical numeric longitudes at a location remote from Greenwich caused 0° of longitude on an Earth-centered ellipsoid to be 5.3” east of the astronomic Greenwich prime meridian through the Airy transit circle.
At the latitude of Greenwich, this amounts to 102.5 metres.
# Prime Meridian passes through following regions/countries: > Arctic Ocean 1. UK (London, Greenwich) 2. France 3. Spain 4. Algeria 5. Mali 6. Burkina Faso 7. Togo 8. Ghana > Atlantic Ocean > Antarctica (Queen Maud Land, claimed by Norway)
Prime Meridian @ UJJAIN 75°47’E was used from 4th century CE Indian astronomy and calendars
