Mexico’s Volcanic Axis

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Apr 192012

Mexico’s active seismic zones have created numerous volcanoes, many of which are still active. Virtually all the country’s active and recently dormant volcanoes are located in a broad belt of high relief which crosses Mexico from west to east: the Volcanic Axis (see map).

volcanic-axisAltitudes in this region vary from a few hundred to several thousand meters. The principal peaks are shown on the map. They include many of Mexico’s most famous mountains, such as Popocatepetl and Iztaccihuatl, near Mexico City; Pico de Orizaba, Mexico’s highest peak; Paricutín, the only completely new volcano in the Americas in recent times; and Colima, considered the most active at present. Many of the volcanoes are surprisingly young. For instance, a study using Carbon‑14 dating on the palaeosols (ancient soils) under 12 volcanoes in the Toluca area yielded ages ranging from 38,600 to 8400 years before present.

It is unclear precisely why this broad belt of Mexico should be so active. Elsewhere in the world all major tectonically active areas have been linked in terms of their location to the margins or meeting‑zones of tectonic plates. Some Mexican geologists believe that Mexico’s Volcanic Axis is a rare example of activity associated with a gently dipping plate margin, one where the edge of the Cocos plate is subsumed, but at only moderate gradient, beneath the North American plate.

Almost all the volcanic activity in this zone has taken place in the last 25 million years, from the upper Oligocene period, through the Miocene and Pliocene and up to Recent. Two distinct periods of activity are recognized by some geologists. The first, in the late Oligocene and early Miocene, produced volcanic rocks often found today tightly folded by later earth movements. The second, responsible for all the major composite cones as well as dozens of ash and cinder cones, started in the Pliocene and continues today.

Erosion has had relatively little time to work on these “new” volcanic peaks, some of which are still developing. As a result, this region includes Mexico’s highest mountains, reaching over 5500 m or 18,000 ft.

Thick, lava-rich volcanic soils make this one of the most fertile areas in North America. Though the relief is very rugged, this area has supported relatively high population densities for hundreds of years, including the current large metropolitan areas of Mexico City, Guadalajara and Puebla. Legacies of previous volcanic activity are found in craters, mud‑volcanoes, geothermal activity, and the numerous hot springs (and spa towns) scattered throughout the Volcanic Axis.

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How has the movement of tectonic plates affected Mexico?

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Apr 122012

In a previous post, we identified the tectonic plates that affect Mexico. In this piece, we look at some of the major impacts of Mexico lying on or close to so many different plates.

To the east of Mexico, in the last 100 million years, outward expansion from the Mid-Atlantic Ridge (a divergent boundary) first pushed South America ever further apart from Africa, and then (slightly more recently) forced the North American plate (and Mexico) away from Eurasia. The Atlantic Ocean continues to widen, expanding the separation between the New World and the Old World, by about 2.5 cm (1 in) each year.

Mexico's position in relation to tectonic plates

Mexico's position in relation to tectonic plates.Map: Geo-Mexico.com; all rights reserved

Meanwhile, to the west of Mexico, an analogous situation is occurring in the Pacific Ocean, where the Cocos plate is being forced eastwards away from the massive Pacific plate, again as a result of mid-ocean activity. The Cocos plate is effectively caught in a gigantic vice, its western edge being forced ever further eastwards while its leading eastern edge smacks into the North American plate.

The junction between the Cocos and North American plates is a classic example of a convergent plate boundary. The collision zone is marked by a deep ocean trench, variously known as the Middle America trench or the Acapulco trench. Off the coast of Chiapas, this trench is a staggering 6662 m (21,857 ft) deep. The trench is formed where the Cocos plate is forced to dive beneath the North American plate.

As the Cocos plate is subducted, its leading edge fractures, breaks and is partly re-melted into the surrounding mantle. Any cracks in the overlying North American plate are exploited by the molten magma, which is under immense pressure, and as the magma is forced to the surface, volcanoes form. The movement of the plates also gives rise to earthquakes. The depth of these earthquakes will vary with distance from the deep ocean trench. Those close to the trench will be relatively shallow, whereas those occurring further away from the trench (where the subducting plate is deeper) will have deeper points of origin.

As the plates move together, sediments, washed by erosion from the continent, collect in the continental shallows before being crushed upwards into fold mountains as the plates continue to come together. A line of fold mountains stretches almost continuously along the west coast of the Americas from the Rocky Mountains in Canada past the Western and Southern Sierra Madres in Mexico to the Andes in South America. Almost all Mexico’s major mountain ranges—including the Western Sierra Madre, the Eastern Sierra Madre and the Southern Sierra Madre—formed as a result of these processes during the Mesozoic Era, from 245 to 65 million years ago.

However, no sooner had they formed than another momentous event shook Mexico. About 65 million years ago, a giant iridium-rich asteroid slammed into the Gulf of Mexico, close to the Yucatán Peninsula, causing the Chicxulub Crater, and probably hastening the demise of the dinosaurs. An estimated 200,000 cubic km of crust was pulverized; most of it was thrown into the air. The resulting dust cloud is thought to have contributed to the extinction of up to 50% of all the species then on Earth. Not only did this event have an enormous impact on all life forms on Earth, it also left a legacy in the Yucatán. The impact crater is about 200 km (125 mi) across. Its outer edge is marked by a ring of sinkholes (locally known as cenotes) and springs where the fractured crust provided easy access to ground water. These locations include the ria (drowned river valley) of Celestún (now a UNESCO Biosphere Reserve), where fresh water springs mingle with salt water to create an especially rich habitat for birdlife.

In the 65 million years since the asteroid impact (the Cenozoic period), the remainder of Mexico has been formed, including many of the plateaus and plains, and the noteworthy Volcanic Axis, which owes its origin to still-on-going tectonic activity at the junction of the North American and Cocos plates.

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Mexico’s political system at the state and municipal levels

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Apr 072012

In a previous post – Mexico’s political system: the basics – we looked at the country’s federal political system. In this post, we look at how the political system works at the two other levels of government: state and municipal.

According to the Constitution of 1917, powers not granted to the Federal Government are reserved for the states. State constitutions roughly mirror the federal constitution. Each state has a popularly elected governor who serves one six-year term and cannot be re-elected. The popularly elected members of the state chamber of deputies serve three-year terms. Non-sequential re-election is permitted. Governors generally have more power than the chamber of deputies. State governments depend on the Federal government for much of their revenue, some of which they funnel to municipal governments. Each state has a Supreme Court of Justice with judges appointed by the state governor.

States are divided into municipalities. There are currently 2458 municipalities (counting Mexico City’s delegaciones or boroughs as municipios) which vary greatly in size and population. For example, the average population of Oaxaca’s 570 municipalities is about 6000 while the average population of Baja California’s five municipalities is over 500,000. Each municipality elects a new president and local council every three years.

Municipal governments have taxing authority but rely very heavily on financial support from state and federal sources. Municipalities are responsible for a variety of public services, including water and sewerage; street lighting and maintenance, trash collection and disposal, public safety and traffic, supervision of slaughterhouses, and maintenance of parks, gardens and cemeteries. Municipalities are also free to assist state and federal governments in the provision of elementary education, emergency fire and medical services, environmental protection and the maintenance of historical landmarks.

Which tectonic plates affect Mexico?

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Apr 022012

The theory of plate tectonics suggests that the earth’s crust or lithosphere is from 5 to 65 km (3 to 40 mi) thick and divided into about a dozen large tectonic plates, tabular blocks that drift across the Earth in different directions and at various speeds (up to a few centimeters or inches per year), probably as a result of thermal convection currents in the Earth’s molten mantle. Most plates consist of a combination of both ocean floor and continent, though some are entirely ocean floor.

Each tectonic plate is moving relative to other plates. The movements are not independent because the plates smash into and scrape against one another. Areas in the center of tectonic plates, far from the boundaries, have relatively little seismic activity, but the boundaries between plates are seismically very active, creating earthquakes and volcanoes. The level of seismic activity depends on the relative speed and direction of the plates at the boundary.

There are three distinct kinds of boundaries between plates. At divergent boundaries, along mid-ocean ridges, plates are being steadily pushed apart, with new crust being added by volcanic activity to the rear of each plate as it moves. At convergent boundaries, plates collide and parts of the plates either buckle or fracture or are subducted back down into the molten mantle. The third kind of boundary is where plates are neither created nor destroyed but are moving side by side. The resulting friction as they rub against each other can produce large earthquakes.

Almost all of Mexico sits atop the south-west corner of the massive North American plate (see map). Immediately to the south is the much smaller Caribbean plate. The North American plate extends westwards from the Mid-Atlantic Ridge, which runs through Iceland and down the middle of the Atlantic Ocean, to the western edge of North America. In a north-south direction, it extends from close to the North Pole as far south as the Caribbean.

Mexico's position in relation to tectonic plates

Mexico's position in relation to tectonic plates.Map: Geo-Mexico.com; all rights reserved

While most of Mexico rests on the North American plate, it is also influenced by several other plates.

The Baja California Peninsula is on the gigantic Pacific plate, which is moving northwest and under the North American plate. The intersection of these plates under the Gulf of California causes parallel faults which are part of the famous San Andreas Fault system. Thus, the Gulf of California is an area of heavy seismic activity.

The small Rivera plate, between Puerto Vallarta and the southern tip of Baja California, is moving in a southeasterly direction and rubbing against the Pacific plate; it, too, is moving under the North American plate.

The Cocos plate and tiny Orozco plate are ocean crust plates located off the south coast of Mexico. The collision of the Cocos plate and the North American plate has had several far-reaching consequences, including both the disastrous 1985 earthquakes that caused such severe loss of life and damage in Mexico City and the much more recent 2012 earthquake that, fortunately, was far less destructive.

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Mar 312012

In a few months time, Mexicans go to the polls to elect a new President. Just how does the Mexican political system work? As a build-up to the important federal elections coming shortly, this post looks at the background to Mexico’s political system and provides a quick summary of the federal level of government. A future post will look at the state and municipal levels.

The current political system in Mexico derives from the Constitution of 1917 which emerged from the Mexican Revolution. The Constitution is a sweeping document that captures the ideals of the Revolution, but also reflects three centuries of Spanish colonial rule. The Constitution is “revolutionary” in that it aggressively protects the rights of workers, peasants and their organizations. It guarantees the right to organize, an eight-hour work day, the rights of female and child workers, and the payment of a minimum wage sufficient to satisfy the necessities of life. The colonial influences are evidenced by highly codified civil law, acceptance of heavy state involvement in civic affairs and business, and the relative strength of the executive over other branches of government. Another important influence is Mexico’s 19th century history which included foreign military occupations, loss of half the national territory and several virtual dictatorships.

The government of the United Mexican States has three branches: executive, legislative, and judicial.

The executive branch is by far the most important and most powerful. The President serves a six-year term, may never be re-elected, and appoints the 18 cabinet secretaries who run their respective secretariats or ministries. The full cabinet meets only rarely. Legislation must be signed by the President to become law. Though the legislature may override a veto, the Constitution dictates that laws can only be enacted after being signed by the President. The President has the power to issue basic rules (reglamentos) independent of the legislature. In fact, most Presidents unilaterally issue more Mexican laws than are passed by the legislature.

The legislature consists of a Senate and a Chamber of Deputies. The 128 senators serve the same six-year term as the President and cannot be re-elected. Each state and the Federal District has two senators from the party getting the most votes in that state and one from the party getting the second most votes.

These 96 senators do not represent equal numbers of constituents. Smaller states have greater representation. For example, in the State of Mexico there are about 4.7 million people per senator whereas in Baja California Sur there are only about 170,000 people per senator. The remaining 32 senators are elected by proportional representation based on the percentage of the national vote obtained by each party. These senators do not have geographical constituents.

There are 500 deputies in the Chamber. Geographic districts directly elect 300 deputies; the remaining 200 are elected by proportional representation. A party must win at least 2% of the national vote to get a deputy in the Chamber. They serve three-year terms and cannot be re-elected.

The ban against re-election means that every three years there is an entirely new Chamber of Deputies. Every six years Mexico has a new President and all new legislators. The ban on re-election diminishes the continuity as well as the overall experience and expertise of Mexican government at all levels.

The judiciary is divided into federal courts and state courts. The federal courts have jurisdiction over constitutional issues, most civil cases (contracts, labor issues, banking and commerce) as well as major felonies (bank robberies, kidnapping), except murder. State courts handle murders, divorces and minor felonies. The Supreme Court consists of 26 judges, selected by the President and confirmed by the Senate. Legally, they serve for life but actually submit their resignation to the new President every six years. Below the Supreme Court are four chambers of judges dealing with criminal, civil, labor and administrative issues. There are 16 federal circuit courts and 68 district courts.

Are homicide rates in Mexico increasing? Perhaps, but…

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Aug 252011

This question is far more complicated to answer than might initially appear. To start with there are two primary sources of homicide data in Mexico which provide very different results and vary significantly from state to state and year to year.  The National System of Public Security (SNSP) compiles homicide statistics from police reports and investigations.  The National Institute of Statistics and Geography (INEGI) obtains homicide data from death certificates reported through the Ministry of Health. For 2010, SNSP reported 35,053 homicides in Mexico, while INEGI – Reporta el INEGI más de 24 mil muertes en 2010 – reported 24,374 homicides.

For a very interesting comparison (in Spanish) of trends over time for these two data sources, including a detailed look at the trends in some individual states, see:

For two earlier posts using SNSP data, see:

What factors may explain why the data is so different?

The terminology associated with homicides is very complex. This is equally true in English and Spanish. Even the basic subcategories do not necessarily match closely from the legal system in one country to that in another. Legal definitions and classifications depend in part on subjective decisions by officials concerning such things as the perpetrator’s motive, intent and state of mind.

In general terms, homicide (homicidio) means the deliberate killing of one person by another. A homicide may be either an:

  • intentional homicide or murder (homicidio doloso) or an
  • involuntary homicide, negligent homicide or case of manslaughter (homicidio culposo)

In some jurisdictions, intentional homicides are further divided into such categories as “first degree murder” and “second degree murder”.

The data associated with homicides are at least as complicated as the legal definitions. Statistics originating from police records will never exactly match those coming from death certificates or public records. For instance, some individuals may have been recorded originally as dying from accidents, natural causes or suicide on their death certificates, but then shown later to have been intentionally killed (murdered) and therefore counted in police records as murder victims. There are numerous possible scenarios in which the police data will differ from the data recorded on death certificates.

Differences in terminology, definitions and application may explain some of the differences in the two data sets, but is very unlikely to explain 100% of such significant differences, so care is needed before drawing any conclusions about Mexico’s homicide rate.

What do the figures for homicides suggest?

In 2000, INEGI, Mexico’s National Statistics Agency, recorded 10,743 homicides in Mexico. This number dropped gradually to 8,897 in 2007 before jumping up to 14,006 in 2008, 19,803 in 2009 and leaping  23% in 2010 to 24,374. Current information suggests the number of homicides will be at least as high in 2011.

The SNSP data have become significantly higher than INEGI data in recent years. They also show an increase in the number of homicides in 2010 (compared to 2009), but of only 11%.  Both data sets indicate a rapid increase. This is especially troublesome given that murder rates had declined rather steadily up until the “drugs war” started in earnest in 2007.

If we average the INEGI and SNSP numbers, it suggests that the overall 2010 homicide rate was about 27 per 100,000 population.

How does Mexico’s murder (intentional homicide) rate compare to that in other countries?

Wikipedia’s list of intentional homicide (murder) rates claims that Mexico’s murder rate in 2010 was 15 per 100,000. SNSP data for Mexico show 2010 figures of 18 per 100,000. Either of these figures is very high compared to Canada (1.6 per 100,000), Peru (3.2) or the USA (5). On the other hand, Mexico’s homicide rate is rather low compared to Honduras (78), El Salvador (65), Venezuela (48), South Africa (34) and Brazil (25). In 2007, Mexico’s murder rate was about 8.4 per 100,000, very close to the world average.

How many of Mexico’s murders are drug-war related?

Data released last January by the Mexican government indicated that drug-war deaths increased in 2010 by 5,659 from 9,614 to 15,273. These data suggest that 63% of Mexico’s intentional homicides in 2010 were related to drug violence compared to only 49% in 2009, 28% 2007 and roughly 10% in 2006. In fact, non-drug-war-related intentional homicides in Mexico appear to have declined 11% from 10,189 in 2009 to 9,101 in 2010, less than the total number of homicides in any year from 2000 through 2006.

This brings us back to our original question, “Are homicide rates in Mexico increasing?” Yes, they are increasing, but only as a result of the much publicized “war on drugs”. It is likely that if there was no drugs war, then Mexico’s homicide rate would be continuing to decline, consistent with its long-term trend.

Related posts, relying on data issued by the Office of the President of Mexico:

The troubled rise of the Green Movement in Mexico

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Aug 012011

Two specific events helped stimulate the rapid growth of Mexico’s green movement in the 1980s:

These motivated many citizens to take direct action. Membership in Environmental Non-Governmental Organizations (ENGOs) surged, as “green brigades” aided the victims. Two months after the earthquake, representatives from 300 regional groups met and formed a coalition of green groups focused on issues such as deforestation, pollution, and opposition to nuclear power. The 1992 Rio UN Environmental Summit and opposition to NAFTA (because it neglected environmental issues) provided additional stimulus to the movement.

The number of ENGOs increased from fewer than 30 in 1985 to about 500 by 1997 when about one in twenty Mexicans was a member of an ENGO.  The ENGOs had highly professional staffs and were well funded from Mexican and international sources. Through demonstrations and militant actions they successfully stopped the construction of a half billion dollar tourism complex south of Mexico City and the proposed world’s largest salt mine in Baja California. They also were significant in the passage of new laws for environmental protection, reducing deforestation, protecting wildlife, and establishing protected areas.

Vicente Fox, the PAN/Green Party candidate, won the Presidency in 2000.  His Minister of the Environment, Víctor Lichtinger, brought scores of highly qualified fellow key ENGO leaders into the administration. While this put the nation’s leading environmentalists on the inside, it also essentially “decapitated” and deflated the ENGO movement, especially its more militant members. Despite these key appointments, Fox’s administration gave relatively low priority to environmental issues. When Fox sided with tourism investors, and decided against issuing a detailed analytical report on beach pollution, Lichtinger and many of his senior staff resigned. They mostly moved to international or academic positions and consequently did not rejuvenate the leadership of the ENGOs they had left.

Green party logo

Green party logo

For the 2006 election, the Green Party formed an alliance with PRI and came in a weak third. The party, which has suffered from despotism, bribery and violation of election laws, managed to elect 22 diputados in the 2009 election. The Calderón Presidency has obtained good environmental marks for its leadership in global warming; however its comprehensive tree-planting program has received some criticism. Current ENGO activity is focused less on high profile mass mobilizations and protests, and more on specific issues such as legislative  lobbying, public awareness, climate change, energy issues, water, deforestation, biodiversity, recycling and local tree=planting and clean-up campaigns.

Main source: Jordi Díez, “The Rise and Fall of Mexico’s Green Movement”, European Review of Latin American and Caribbean Studies 85, October 2008, 81-99.

Mexico’s environmental issues are analyzed in many chapters of Geo-Mexico: the geography and dynamics of modern Mexico, including chapter 30. Explore the book using Amazon.com’s Look Inside feature and buy your copy today!

Mexico’s Pemex: the government cash cow that environmentalists love to hate

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Jul 252011

Petroleos Mexicanos (Pemex), the giant, state-owned petroleum company, is a symbol of national pride with revenues of over $100 billion in 2008. However, it is cash poor because most of its revenue goes to the government, covering 40% of the national budget. Pemex is $40 billion in debt and its maintenance budget is insufficient to keep its old infrastructure operating safely. About a third of Pemex’s 50,000 km of pipeline is over 30 years old and susceptible to failure.

Environmentalists love to hate Pemex because it has inflicted enormous environmental damage. The June 1979 blowout at the Ixtoc-I drilling rig in the Bay of Campeche resulted in the world’s second largest ever unintentional oil spill: over 450,000 tons, surpassed only by BP’s Deepwater Horizon, but more than ten times the size of the 1989 Exxon Valdez disaster. In November 1984 a series of explosions at a Pemex storage facility in San Juan Ixhuatepec in northern Mexico City started major fires killing about 500 people.

A massive gasoline leak into Guadalajara’s sewers in 1992 resulted in a series of explosions that resulted in over 200 deaths. In recent years numerous smaller, but still fatal, explosions and pipeline failures flooding rivers with oil have brought new attention to Pemex’s environmental damage and failing infrastructure.

cover of "como destruir el paraiso"

It has long been recognized that environmental damage is particularly severe near the conglomeration of Pemex facilities in southern Veracruz near the mouth of the Coatzacoalcos River. The river suffers from chronic heavy petroleum pollution, receiving massive doses periodically when pipelines break. Possibly the only beneficial outcome of the decades of widespread damage caused by Pemex in its principal areas of operation in Veracruz, Tabasco and Campeche was that it prompted the publication in 1983 of Cómo destruir el paraíso (How to destroy Paradise), a book which gave an immense boost to Mexico’s then fledgling environmental movement.

Federal environmental agencies have had only limited success in forcing Pemex to take corrective actions. Pemex recognizes the problems and applies each year for more maintenance funds from the government. The government, however, sets a higher priority on funding exploration since Mexico’s oil reserves are running out. Pemex is fundamental to the Mexican economy but needs investment in maintenance and must become more accountable for its environmental impacts.

Mexico’s environmental issues are analyzed in many chapters of Geo-Mexico: the geography and dynamics of modern Mexico, including chapter 30. Explore the book using Amazon.com’s Look Inside feature and buy your copy today!

How will reduced out-migration impact Mexico’s total population?

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Jul 192011

As described in an earlier post –Is massive Mexican migration to the USA a thing of the past?– we examined a 6 July 2011 New York Times article which indicated that Mexican migration to the USA had slowed to barely a trickle. If this is correct, Mexico’s population will be considerably higher in future years. This post estimates what this impact will be.

In another post –Projecting Mexico’s population: when, if ever, will it stop growing? – we incorporated the results of Mexico’s 2010 census and 2008 migration estimates into the most recent official population projection available from the Mexican Government’s CONAPO (Spanish acronym for National Population Commission). This analysis indicated that Mexico’s population would peak at 140.5 million in 2043, rather than the 130.3 million indicated in the older CONAPO projection.

If net migration becomes zero in the future, as suggested in the New York Times article, Mexico’s population will peak at 149.3 million in 2051. If net migration in future years is between the 2008 estimate of 203,000/year and zero, say 100,000/year, then the Mexican population will peak at 144.9 million in 2049. Clearly, the variation in these projections of almost nine million (149.3 verses 140.5) is quite significant. Given these different projections, our current thinking is that Mexico’s population will probably peak at around 145 million about mid-century.

Though population projections based on birth and deaths rates tend to be fairly accurate, net migration projections are far more precarious. Actual net migration between the two countries will depend on a wide range of future socio-economic variables for both countries. The most obvious of these variables will be fertility rates, growth of the working age population, education opportunities, economic growth, trade regulations and trends, job availability, unemployment rates, and personal preferences of both workers and retired people. There undoubtedly will be surprises such as technology changes or climate change. Some of these may have very profound impacts on migration, and therefore on total population levels.

Migration between Mexico and the USA is the focus of chapters 26 and 27 of Geo-Mexico: the geography and dynamics of modern Mexico. Explore the book using Amazon.com’s Look Inside feature; buy your copy today!

The spacing of central places in Mexico

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Jul 162011

Central place theory may work quite well in Mexico in terms of the relative numbers of settlements of different size, but the theory also suggests that those places on the same level of the urban hierarchy should form a distinctive spatial pattern and be roughly equidistant from one another. In essence, this means that each of these central places will be at the center of an approximately equally sized market area, or sphere of influence, well positioned to serve everyone who lives within its limits.

The application of central place theory to Uruapan, Michoacán

The application of central place theory to Uruapan, Michoacán. Credit: Tony Burton / Geo-Mexico; all rights reserved

The map shows the settlements in the western part of the state of Michoacán. The largest city by far is Uruapan (250,000 inhabitants in 2008). Around Uruapan are six fairly large neighboring towns or cities. Each of these settlements has its own corresponding market area. However, even though these six places are roughly equidistant from Uruapan, they turn out to be very different in size. For example, Zamora (240,000) has more than four times the population of Pátzcuaro (53,000). Zamora is bigger because in addition to providing services to a larger, more prosperous, surrounding market area, it also has some manufacturing and is on a railroad line and the original highway between Mexico City and Guadalajara.

In addition, there is no observable regularity in the pattern of settlements of the two smaller sizes—“other towns” and “urban localities”—shown on the map. This is clearly in contradiction to central place theory, but should not really be a surprise. The theory assumes, for the sake of simplicity, that large areas will not have any significant differences in relief or soil fertility and that transport costs will be directly proportional to distance. It also assumes that rural areas have equal population densities and that their residents have similar consumer tastes and purchasing power. In practice, these assumptions are not valid, and some of the anomalies in the pattern of settlements shown on the map can be easily explained. For instance, the areas immediately north of Apatzingán and east of Nueva Italia are very mountainous, far less favorable for farming and settlement than the area north of Uruapan.

The very idea that settlements will be equidistant from one another begs a very important question, pertinent to our earlier discussion of the categories of rural settlements. Should we measure distance only in a spatial sense, in kilometers, or might it be more worthwhile to consider it in terms of the time or monetary cost required to make a particular journey, taking into account the terrain and transportation network?

In summary, central place theory does a good job of explaining the number of central places at each level and the types of services they provide. At the same time, departures from the idealized shape and size of market areas predicted by the theory help to reveal the complexities of Mexico’s physical, human and socio-economic geography.

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