Philadelphia, Pennsylvania, is located near 40° north latitude and 75° west longitude. The coordinates of Philadelphia’s City Hall are 39°57’9” north latitude and 75°9’54” west longitude. Global Positioning Systems typically divide degrees into decimal fractions rather than minutes and seconds. Philadelphia’s City Hall is located at 39.952583° north latitude and 75.165222° west longitude.

The meridian that passes through the Royal Observatory at Greenwich, England, is 0° longitude, also called the prime meridian. The meridian on the opposite side of the globe from the prime meridian is 180° longitude. All other meridians have numbers between 0° and 180° east or west, depending on whether they are east or west of the prime meridian. The equator is 0° latitude, the North Pole 90° north latitude, and the South Pole 90° south latitude. Specific locations can be identified as the point where a parallel intersects a meridian. A location can be designated more precisely by dividing each degree into 60 minutes (') and each minute into 60 seconds (").

Measuring latitude and longitude is a good example of how geography is both a natural science and a study of human behavior. Latitudes are scientifically derived by Earth’s shape and its rotation around the Sun. The equator (0° latitude) is the parallel with the largest circumference and is the place where every day has 12 hours of daylight. Even in ancient times, latitude could be accurately measured by the length of daylight and the position of the Sun and stars.

On the other hand, 0° longitude is a human creation. Any meridian could have been selected as 0° longitude because all meridians have the same length and all run between the poles. The 0° longitude runs through Greenwich because England was the world’s most powerful country when longitude was first accurately measured.

Inability to measure longitude was the greatest obstacle to exploration and discovery for many centuries. Ships ran aground or were lost at sea because no one on board could pinpoint longitude. In 1714, the British Parliament offered a prize equivalent to several million in today’s dollars to the person who could first measure longitude accurately.

Most eighteenth-century scientists were convinced that longitude could be determined only by the position of the stars. English clockmaker John Harrison won the prize by connecting longitude and time. He invented the first portable clock that could keep accurate time on a ship—because it did not have a pendulum (Figure 1-22). When the Sun was directly overhead of the ship—noon local time—Harrison’s portable clock set to Greenwich time could say it was 2 P.M. in Greenwich, for example, so the ship would be at 30° west longitude because each hour of difference was equivalent to traveling 15° longitude. John Harrison’s first chronometer, weighed 75 pounds.

John Harrison crafted four versions of the Chronometer each an improvement over the previous version.

H4 (Version 1) H3 (Version 2) H4 (Version 3) H1 (Version 4)

Types of Maps

Maps can represent the distribution of data for one or more variables in a variety of ways:

An isoline map connects with lines all the places that have particular values

You may be very familiar with these types of maps they are used widely in meteorology to show how hot different areas of the country are.

A dot distribution map depicts data as points and shows how those points are clustered together or spread out over an area. Each dot represents a predetermined number of observations, which could be one or many

There are a variety of ways to use dot distribution maps

Replacing Towns With Dots

Using the dot methodology, it means New York City is the same size as Anytown, USA. This seems crazy, right?

Although this is surely a drawback, the results are still pretty interesting. After all, hubs like New York City are centers of commerce and culture, and they are surrounded by hundreds of other nearby towns.

Let’s take a look at (most of) North America:

A few things that are noticeable right away?

You can see the difference in topography between the plains and the more mountainous part of the continent. In flatter places like Nebraska or Saskatchewan, the towns are evenly spread out – and in regions with uneven geography, such as Colorado or British Columbia, towns are typically located in the valleys.

Further, the density in the Northeastern part of the United States and surrounding the Great Lakes work to provide quite a contrast to the emptier parts of the continent.

Natural features like the Everglades are also quite easy to spot on the map – it’s one of the only non-populated areas in an otherwise dense Florida. If you look at the northwestern tip of Wyoming, you’ll also see a lack of dots in the 2 million acres of Yellowstone National Park.

Europe and MENA

Now let’s go across the Atlantic – here’s a map of Europe, North Africa, and most of the Middle East.

This map is also pretty spectacular – you can see the cities along the Nile, the “eye” of Moscow, and impressive amounts of population density in places like Belgium, Holland, Germany and Switzerland.

World View

While we haven’t seen a world map using this method, it’s not hard to imagine what places like India, China, Japan, or Bangladesh could look like with dots replacing each town within their borders.

These are the densest parts of the world – to even more extreme levels than the denser parts of Europe shown above. To show density a different type of map is used a Choropleth map.

A choropleth map is a map where recognizable areas are shaded or patterned in proportion to the measurement of the variable. For example, areas with darker colors may represent the highest range of the data

Here’s a more standard population density map, using people per square kilometer, to give you an idea:

A graduated symbol map displays symbols that change in size according to the value of the variable. A higher value is typically represented by a larger symbol

But how proportional symbol maps are different from graduated symbol maps is that symbology is unclassed. In other words, proportional symbol maps scales dots with absolute magnitude.

A cartogram is a map in which the size of a country or U.S. state is proportional to the value of a particular variable, such as the amount of corn produced, rather than to the actual land area. The cartogram in preserves the rough shapes and positions of the states, but distorts their scale: Iowa is much larger than Texas because Iowa produces a lot more corn.

These types of maps generally keep the shape of the map but the distortion itself relays information.