Map composition

Map Composition is the process of bringing together the various symbols on a map so that they work together to form a desired Gestalt, or whole effect. The term is generally applied to the combination of layers of geographic symbols in the map image itself; the inclusion of additional elements such as titles, legends, and scale bars is referred to as Map layout. Quality composition is crucial to creating a map that is both functionally effective and aesthetically pleasing. Most of the principles and techniques of composition are based on the concept of Gestalt, in which that all of the elements of an artistic work (for example, a map) are perceived by viewers as a whole, so that viewers will develop a general judgment of the map, whether positive or negative.

Gestalt Goals
To create a map that is both useful and beautiful, the cartographer has many goals in mind during the composition process. Some of these goals are specific to a particular audience, purpose, or style, but there are also goals common to most maps. Gestalt aims to aid the map's overall composition by applying fundamental categories of harmony, contrast, and visual equilibrium. The following are gestalt judgments of map quality that are generally desirable:
 * Clarity: the intended purpose of the map is obvious to map readers, and each reader can easily find the relevant information without being distracted by "clutter."
 * Professionalism: the map appears to have been crafted with skill and care, leading to a greater trust of the cartographer's ability and therefore the information portrayed in the map.
 * Harmony: the different map symbols blend together well, appearing to work together to achieve a single purpose rather than competing.
 * Beauty: the map "looks good" as a whole. Map readers should have a positive initial reaction and should be willing to study the map long enough for it to achieve its purpose.
 * Informative: maps are inherently good at portraying large volumes of data in a single image. The more information a map contains, the more readers can glean from it.

Sometimes these goals may appear to be in opposition. For example, a map loaded with data can easily appear cluttered, and one may be tempted to achieve clarity by discarding most of the information. Quality composition involves finding creative solutions that balance multiple goals simultaneously.

Layers
Map composition is all about organization, organizing layers so that they work with each other and then together on a layout is an important part of map composition. The individual layers that make up a map are just as important as the map itself. When composed correctly, layers can work together to form the picture that the map composer is trying to portray. When composed incorrectly layers can be disorienting, confusing, and counterproductive.

Layers display GIS data using user set symbology, layer data consists of either raster datasets or vector (points, lines and polygons) datasets. A polygon layer should never be placed on top of a line layer, and a line layer should go under a point layer. Knowing exactly what story or information the map is supposed to display and understanding the hierarchy of the layers will help to organize the layers properly so that the correct story and information can be shared.

Principles
Effective composition is governed by several theories of how multiple symbols are perceived collectively. In visual design (including cognate disciplines such as architecture and cartography), the following principles of good composition are generally accepted:


 * Unity is achieved when all of the parts of the map work together to form a single whole or Gestalt. If unity is not achieved in a map, readers can have an impression of the map being cluttered, confusing, or complex.
 * Balance is a sense of visual equilibrium that is analogous to physical balance using the relative position and weight of physical objects. A work with equal weight on the left and right, and on the top and bottom, is perceived as balanced.
 * Proportion is a judgment of the size of elements of the work relative to the reader's judgment of how large they should be. While the size of map features is often fixed, Map projection plays a role in achieving good proportion, and it is an important principle of Map layout. When proportion is violated, such as in a Cartogram, the resultant shock can add interest.
 * Rhythm is the guiding of viewers through an intended sequence of reading the work. In a map, this intended sequence is typically tied to the map purpose. Judicious design and placement of elements of a Map layout, especially the MapTitle and Map legend, aid rhythm.
 * Emphasis, commonly called Visual Hierarchy in cartography, is the apparent order of importance of symbols perceived by the human eye, which is generally expected to match an intended order of importance of the phenomena being represented. A Hierarchy can be achieved by applying different weights, sizes, and color saturation.

Some of these principles have further developed as techniques in Cartography.

Contrast
Contrast in map design refers to making different map symbols visually distinguishable from one another and their background; good contrast aids composition principles such as balance, emphasis, and rhythm. Poor contrast will make it difficult to understand the purpose of the map. Contrast can be created by manipulating any of the visual variables: light vs. dark, red vs. blue, thick vs. thin, large vs. small, etc.

Color contrast can be measured as a ratio, which can help a cartographer make decisions about which colors to use. Certain features will stand out more (usually lighter or darker) when the contrast is high. On the other hand, a low contrast between features will display a sense of togetherness and uniformity on a map.

Visual grouping
Visual grouping is a filtering process by which map readers isolate a particular kind of symbol from the rest of the visual field, and can thus see the patterns in all of the individuals represented by that symbol. It is an aspect of rhythm, as it aids the process of map reading. There are various ways that the elements of a map might be grouped in a map reader's mind. For example, they might focus on elements that are close to each other on the map, they might look at elements with the same symbols in different parts of the map, they could focus on continuous elements (such as tracing out a route on a road map), etc. The cartographer should keep this tendency of visually grouping in mind when creating their map.

Interposition
Interposition is an artistic cue in which one object obscures another and thus appears to be in front of it.

Figure-ground contrast
Figure-ground contrast on a map is the distinction between one or more objects of interest (the figure) and the remainder of the map (the ground). Using figure-ground contrast is an effective technique to focus the map reader's attention on the most important elements of the map. For this technique to be effective, the map should be composed with a few principles kept in mind. The figure should be easily differentiated, which can be accomplished by making it visually distinct, such as by making it a brighter color. The figure should be closed, which means that it can be distinguished as a single object. The figure should be near the center of the map. Articulating the border of the figure and making sure that it is easy to follow the lines will also help the figure stand out.

Negative space
Negative space is the empty space that surrounds or is between the subjects of an image. It may be incidental, created by the inherent shape of the figures, or it may be designed strategically to organize the map elements. Effective use of negative space is an important technique in map composition because it can make the map more organized, clearer, and more attractive by emphasizing the primary subject of the map. For example, a map that has the ocean as its primary subject can use the land as negative space by leaving it blank. Similarly, if a map is focused on some land feature, it can use bodies of water as negative space. This negative space is often a good place to put labels, legends, scales, or other map elements.