Unit 4.3: Cartographic Process

This section introduces and describes the cartographic process.

 

The cartographic process is a series of steps that we follow to go from an unmapped data set to a final mapped form. As cartography is both the art and science of map making, there really is no set process for creating cartographic products. However, there are some best practices, and a recommended series of steps if you’re unfamiliar with designing maps. This section will introduce you to, and discuss, one recommended series of steps you should follow to design a map.

 

This cartographic process has five steps. Is important to note that the steps do not need to happen in exactly this order as cartography is often a dynamic and iterative process. However, some steps you will naturally want to complete first and are listed in the recommended order on the slide. The first recommended step is to define the purpose and meaning of the map. The second recommended step is to choose the scale for the map. Next is to determine the map format, printing limitations, and economics of reproduction of the map product. The fourth step in the cartographic process is to abstract and generalize the data to prepare it for placement on the map. And finally, the fifth step in the cartographic process, is to design the map layout. We will now explore each of the steps in more detail.

 

When we define the purpose and meaning of a map, the goal is to interpret the requirements of the user and to determine what needs to be communicated. Additionally, your job is to determine how to best facilitate communication of your ideas, and create a narrative for the map. It is important to note, that often times, you, and or your customer, may not fully know these requirements at the beginning. Therefore, expect to revisit and redefined the purpose of meeting as you work with the data, and create prototype maps.

 

The second step of the cartographic process is to choose the map scale. Defined, the map scale is the ratio of the map distance to the earth distance. The map scale operates along a continuum from a large scale to a small scale.

 

Broadly speaking, there are three typical map scales. A large scale map covers a small geographic area, and runs from a map scale of 1 to 0 to 1 to 600,000. A medium scale map runs from one to 600,001 to 1 to 2,000,000. And a small scale map covers a large geographic area and runs from one to 2,000,001 to essentially infinity. The large scale maps, since they show such a small portion of the earth, will allow you to show more details, and more features about the earth surface. As you move to medium and small scale maps, you are showing a larger portion of the earth at once, which does not allow for the same amount of detail. Therefore, medium and small scale maps will not have nearly as much detail as large scale maps will.

 

Therefore, as the amount of detail you can show a map is directly dependent upon scale, the selection of map scale is possibly the most important decision a cartographer makes. For instance, if you choose to large of a scale, the map may be so large, that you will need to split it up onto multiple maps. On the other hand, if you choose to small of the scale, you may not be able to show the amount of detail that you wish to show as the map will be “zoomed out” too far.

 

The third step in the cartographic process is to determine formatting, printing, and economics of reproduction. At this point we should be asking ourselves, what kind of map should we be making? How will the map be displayed, and on which medium with a map be produced? And finally, how much will it cost to create the map on the chosen medium? Depending on your answers to these questions, you may find that while you would like to print the map on paper, the map is so large, that it would be too expensive to economically reproduce.

 

The abstract and generalize step of the cartographic process is where you may spend the majority of your time when designing a map. The goal of this step is to prepare your geospatial data in a way that only information that is potentially meaningful to the context of the map should be included. This means, they will need to select and organize your geospatial data in a way that is necessary to communicate the concept to a map reader without including unnecessary information or details. The end result is the reduction of the amount of detail in a map to create a simple, but effective, visual image.

 

There are several methods to abstract and generalize your geospatial data. Selection, classification, simplification, and symbolization. The first method, selection, is where you only use a subset of a geospatial data set on the final map product. The selected data should contain information that is relevant to the message of the map at the chosen scale. The second method of abstraction is classification. Classification is the process of combining observations into bins or classes. The goal of classification is to reduce the number of unique symbols on a map, and to aggregate information to a useful enumeration unit, such as a state, or county. The third method of generalization is simplification. Depending on which scale you chose for your map, you may need to simplify the data so that is more visually pleasing on the map. For example, on the figure of the screen, the blue line is the original very detailed path the river. This data set was probably originally intended to be used on a large scale map. However, we wish to use this river path on a medium scale map, but when we place the river path on a medium scale map, it is so detailed that the river looks cramped, and we are unable to print the fine detail on a piece of paper. Therefore, we simplify the line by reducing its complexity, but still maintaining the character of that river path. This is shown as the red line on the figure. Once the river path has been simplified by reducing the number of vertices, the river now looks good at the chosen scale, and is able to be printed with our printing technology. The fourth method of abstraction and generalization is symbolization. Symbolization is the process of assigning such visual variables as color, shape, size, and orientation, among others. The goal of symbolization is to assign a visual marker to represent the spatial phenomenon being mapped.

 

There are no set rules for how you will symbolize your map, however, there are some strongly recommended conventions that you should consider following. For instance, water should almost always be blue, and land should almost always never be blue. Also, if there is a very common symbol for a feature, for instance a blue circle with a white ‘I’ inside of it stands for information, therefore, you should use that symbol on your map when you want the map reader to know that the feature is where they can get information. One of the great things about cartography is that you can experiment with your design, however, keep in mind, that you need to clearly and succinctly communicate your idea to the maps users.

 

The fifth step in the cartographic process is to design the map layout. There’s much more that goes on a map than simply the data, and we must carefully consider the placement and design of each of these elements.

 

There are 12 elements that compose a map:

1. The first element, the map body, contains the geographic information that is the focus of the message of the map, and should typically be the largest element on a map  layout.
2. The neat line is like a frame for the map, it typically surrounds the entire map, and allows the map to separate itself from the surrounding page or elements. The lines can also surround other map elements to set them apart.
3. An inset map is a smaller map body that shows greater detail for an area on the main map body,
4. a scale bar communicates the ratio at which the earth’s been reduced to be placed on the map.
5. The legend is a map element that lets the user know what each symbol on the map means.
6. The title, typically placed at the top the map, is usually the largest text of the map and provides a short, descriptive, statement about the purpose of the map, and may include  other pertinent information, such as the timeframe for which the map applies.
7. The directional indicator, more commonly known as the North arrow, lets the user orient the map relative to a direction.
8. Metadata is the documentation for the map and the data displayed on the map. Metadata should include items such as the date the map was created, the author of the map, and data sources for the data shown on the map body.
9. Ancillary text
10. Ancillary objects are elements included in the map layout to support the maps message. These may include images of locations or features displayed a locations of the map, charts, graphs, sounds, videos, or simply explanatory text.
11. The graticule references a coordinate, or measurement system, that the map user can use to derive the location, coordinates.
12. Last, labels identify features on the map, typically based on information stored in the features attribute tables.

 

Another thing to consider when designing the layout is the scale, size, and shape of the primary object being mapped, and the media onto which the map will be produced. For instance, if we are mapping Tennessee, we notice that the shape of Tennessee is roughly a wide but not so tall parallelogram. Therefore, we may choose to orient the media in a landscape setting so that Tennessee can use the maximum amount of media as possible. Additionally, we may be constrained by the size and shape of the media. Therefore, if we have been asked to produce a map showing all manhole covers in a city such as Houston, but we are constrained to a paper size of 8.5 by 11 inches, then we know that we must split our map up into potentially hundreds of pages, each showing a small portion of Houston, as we would be unable to show enough detail to show every single manhole cover on a single 8.5 by 11 inch piece of paper.

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