In this module we're going to learn about maps. A map is almost universally a two-dimensional representation of a piece of three-dimensional space. Only with the advent of modern computer graphics, these three-dimensional maps are made possible. The map typically serves two map function. A, they're a spatial database, and B, they're a communication device. And you should also know the science of making maps is called cartography and people who are actually involved in this, they're called cartographers. All right, so what's the learning goal? The learning goal is we're going to look at attributes and features on a map, and then we'll also discuss map scale and coordinate systems, and then we'll also learn a little bit about map projections.
So now let's move on to the feature and attributes in the map. Each row in the attribute table refers to a feature's location on the map with numerous attributes associated with it. In this example, each object refers to a state that includes attribute data, including the information such as FID, the unique identifier shape, for example, the polygon, state abbreviation, AK, AR, Arizona, AZ, and then full state name and a FIPS code, which is basically unique code assigned to each state, and the longitude and the latitude coordinates.
If you remember last week's module, you basically developed a geo database with the features and attributes, and this is exactly what we're looking at. So geographic data represents spatial location, which is essentially a feature and a non-spatial attribute measured at a certain time. Now, for instance, the state, which is a feature with a spatial location, can contain an attribute such as population density, and that's exactly what you actually shown on the map. The population density has a different color. The more dense means you have more darker color, and this is how you actually represent a piece of information, an attribute on a map. Now there are discreet and continuous version of a feature, so a feature can also be categorized and either discrete or continuous. Discrete features are well-defined and are easy to locate, measure and count, and their areas or boundaries are readily defined.
So for example, a discrete feature in a city include buildings, roads, traffic signals, parks, trees, all that good stuff. The continuous feature on the other hand, are less well-defined and exist across space. So the most commonly-cited example of a continuous feature are temperature, for example. It is not discreet because it has a gradient. And elevation. Elevation has a gradient. Changes in both temperature and elevation tend to be gradual over relatively large areas, and that's why they're called continuous feature.
When we are looking at a piece of information, the data attribute on a map, typically this is how you show, with a different color code. For a given location, you can have multiple data attributes. Color codes are used to represent a certain kind of attribute for a specific feature. That feature could be a county or it could be a city, it could be a zip code, it could be a block group. So these are all different feature of a certain location.
Reference maps, it displays the boundaries, names, and unique identifiers of a standard geographic area, as well as a major cultural and physical features such as roads, railroads, coastlines, rivers, and lakes. On the right, you'll see the map, which can be used as a reference map. Whereas the thematic map is concerned with a particular theme or a topic of interest. In this case, we're actually presenting the percentage of participants in sports exercise once a week and the color code represents the percentage of attitude general do some sports and exercise once a week. So it has actually one particular theme and the gradation of that theme is typically shown as a gradation of the color.
So while reference maps emphasize the location of the geographic feature, thematic maps are more concerned with how things are distributed across space. Such things are often abstract concepts such as life expectancy around the world, per capita gross domestic product in Europe, or a literacy rate across India. So again, that would give us a sense how this particular theme is spread across the map.
Now let's talk about a dynamic map. Both reference and thematic maps can be dynamic in nature and such maps are integral component to GIAs as well. So the key point about dynamic map is that more and more people, not just GIA professional, have access to such map. As you can see here, this map is dynamic in nature because it changes the color, A, and the color code actually provides a different piece of information as you can see here.
So what you're seeing here in this map, the sexually transmitted disease, how the disease has changed across a different timeline, across different years. So that's actually another type of map people use and journalists are actually using maps like this to tell a good story.
Now, when we talk about map, we should also talk about map scale, right? It refers to the factor of reduction of the world so it fits in the map. Typically you see the map scale is shown at the bottom of the map. The map scale can also be portrayed graphically with the scale bar like you see here, and the scale bars are usually used on the reference map and allow map users to approximate distance between locations and features on the map. So every map has a scale determining how large objects on the map are in relation to the actual size. A larger scale shows more detail, thus requiring a larger map to show the same area. So a smaller number after a colon means larger scale. So in other words, one is to 10,000 is a larger scale than one is to 25,000.
And we also know you have to use legend to share information in the map. So for example, map legend provides users information about how geographic information is represented graphically. So legends usually consist of a title that describes the map as well as the various symbols. In this example, we're trying to show the 2017 average household income by state. As you can see, different color has different values and that's basically how you understand which state had the highest average household income. So for example, the darker color means they had between 98,000 to 117,000. So that's basically how you read this map.
Now let's look at map coordinate system. The reason why you require a coordinate system, because you need to actually put an object on a map. So the coordinate systems are the framework that are used to define unique position on a map, which is basically on the globe. The coordinate systems that are most commonly used define the location of the three-dimensional earth, which is the geographic coordinate system and it's based on a spheroid. So on the right you see the globe and then the unit that you actually use are, if you define a position, for example, the New Orleans, it has actually a latitude and longitude information. The unit of measure in the GCS is degrees, and locations are defined by the respective latitude and longitude within the geographic coordinate system. So the latitude essentially is the angle that particular point makes from the equator, and the longitude is the angle that it makes from the prime meridian.
So that's basically how you measure a location on the surface of the earth. So the latitude and longitude can be expressed in degrees and minutes. I actually showed you a little website. I would like you to practice and see how often you can actually answer the latitude, longitude question correctly. So it's a good practice to have. So typical nominal location, you usually express it as a name, and then you look at the absolute location, it's at 34 degrees and 3 minutes north and 180 degrees and 15 minutes west. And if you want to actually find out the latitude and longitude absolute location, that would be 34.05 and -118.25. So that's the lat and long. Okay?So this is how you actually find the location of an object. Either you can have an address or you can actually geocode that address to get lat and long. There are certain applications you can try to find the corresponding latitude and longitude for a given address.
Map projections refer to the methods and procedures that are used to transform the spherical three-dimensional earth to two-dimensional planar surfaces because when we look at the map, we typically look at it in a two-dimensional plane. So now the question is if your map is actually about the globe, which is three-dimensional, how can you actually transform that three-dimensional object into a two-dimensional planar surface? Well, this has never been done correctly. You will actually realize any kind of projection from a three-dimensional sphere to a two-dimensional plane, there is actually some sort of a distortion that takes place.
Typically, map projections are mathematical formula that are used to translate latitude and longitude on the surface of the earth to X and Y coordinate on a plane. There are several types of projections people use: the planar, conic, and cylindrical projection. Imagine that you have a little globe and basically you turn the light bulb inside that globe. The shadow that goes on top of the planar, that basically will give you a two-dimensional projection of the map, of the three dimensions. So that's basically called planar projection. The conic projection is you basically get a cone and then put it around the globe and then turn the light on. Whatever shadow that falls on that cone, you open it up, that becomes the comic projection. And then a cylindrical projection is basically get a cylindrical paper, let's say, and then turn the globe and put it around the globe and then turn the light. And whatever shadow you get on the cylindrical plane, you flat it out and then you'll find that projection is actually on that paper. So what you're really looking at is projection, which is not quite perfect.
When we talk about projection, Mercator projection is actually a pretty standard one. This has been around for last 400 years or so. It was created originally by Flemish photographer Gerardus Mercator in 1569, when Antarctica had not even discovered. Mercator was designed as a navigational tool for sellers as it was most convenient to hand-plot courses with parallel rules and triangles on the map. We have been using Mercator for several reasons. So on the Mercator projection, Greenland is roughly same size in Africa, but in reality, Africa is almost 14 times larger. So again, as you can see here, there is a bit of a distortion, but Google Maps and Bings and Yahoo and even OpenStreetMaps, they continue to use same version, which is the Mercator version, or the other version of Mercator to display the world map.
So again, I just wanted to give you a little sense how the maps are actually created and this is really not a perfect solution, but we know that no map is perfect because there is always some sort of distortion. But beyond that, our goal is not to really get too much into the map distortion piece, but rather understand how maps are created and how to really visualize information on the map, how do I actually tell a story using the map. That's basically our focus in this course and we'll continue that beyond this module. All right?
What I want to do now is pause. I wanted to reflect what we actually just learned and see what you can actually do about it. So when we talk about different types of maps and the map projection, how is that applicable to what you're going to do in the real world? Thank you very much.