Labeling (map design)

Cartographic labeling is the craft of placing text on a map in relation to the map symbols, together representing features and properties of the real world. Using text effectively creates maps that are clear, informative, and attractive. It is part of typography which is an essential element of cartographic design.

Purposes and Goals of Map Labels


Text simultaneously serves several purposes on maps such as:


 * Identifying unique features (e.g., The United Kingdom)
 * Placing features within broader categories (e.g., park)
 * Locating features within a general geographic context (e.g., this vegetation stand is within Zion National Park)
 * Explaining the characteristics and meaning of features on the map (e.g., high economic potential zone)
 * Text prescribes and proscribes action (e.g., camping not permitted here)
 * It can add to the aesthetic beauty of a map
 * It can give a map an aesthetic feel (e.g., using a typeface that looks modern or historical)

To be effective, text on a map at least needs to meet two basic goals:
 * 1) Legibility: readers must be able to read the text.
 * 2) Feature Association: readers must be able to recognize to which geographic feature the text is referring, both as symbolized on the map and in the real world.

Legibility and Perceptibility
Legibility in cartography can be defined as the degree to which labels or writing elements on a map are understood by the audience based on the appearance of the text. The conjugation of typeface, weight, size and case defines how effective the legibility of a map is.

On the other hand, perceptibility is the speed at which letters or words can be perceived and recognized. Because the human eye reads text on maps letter by letter and not by word, perceptibility of text on maps is innately hindered. With this in mind choosing type becomes more important; this is because the letters are not displayed as blocks in a text, but rather they may be spread out, curved or interrupted by other features. An important issue that has to be kept in mind when designing a map is the difference between the readability on a computer monitor screen when designing the map and the readability of the physical printed version.

In some cases, the background colors on the map can make labels difficult to read. There are a few different possible solutions to deal with this problem. Sometimes labels can be made more legible by adjusting the colors of the labels or the background layers on the map. For example, making the background lighter can help darker labels stand out better. Another option can be to add a "halo" behind the label, a lighter outline behind the text that helps increase contrast against the background. The general consensus is that halos detract from the design of a map, but they could be effective if the cartographer is not able to otherwise adjust the colors. The cartographer would want a thin halo that blends into the background colors.

In some cases, where it is appropriate to use more than one typeface on a map, it is important to keep the harmony between the different typefaces to encourage a high level of legibility. Usually, two faces, one serif and one sans serif, including the two variations of bold and italic works the best; however, harmonizing the typeface to suit the purpose and the audience should be taken into consideration as well.

Placement
To communicate spatial information effectively, features such as rivers, lakes, and cities need to be labeled. For example, text can be placed by specific features to describe them (such as adding names of major cities to a map). Text can also be placed in the general location in order to draw the user's attention to that specific area on the map (such as the Rocky Mountains). For area features, it is important to curve and extend the spaces to properly fill in the areas enough that the audience can discern different areas.

Over centuries cartographers have developed the art of placing names on even the densest of maps. Text placement or name placement can get mathematically very complex as the number of labels and map density increases. Therefore, text placement is time-consuming and labor-intensive, so cartographers and GIS users have developed automatic label placement to ease this process. Many software features automatically choose label placements for the cartographer, but these are not always a fail-safe option. The use of good judgment and cartographic conventions are important to gain the best placement.

The most widely accepted pattern is to start at the center and work outward towards the northeast quadrant from the point. Many studies have been researched to address the correct strategy for the placements. The point feature cartographic label placement (PFCLP) problem offers the solutions when point boxes overlap.

Guidelines for Labeling
Swiss cartographer Eduard Imhof described these general principles for positioning labels on a map:
 * Names should be legible (labels are usually as horizontal as possible with no upside-down labels)
 * Names should be clearly associated with the features they refer to (i.e., they should be placed in an unambiguous position).
 * There should be no overlap between names and other map content, if at all possible.
 * Names should help the map-reader obtain an understanding of the spatial distribution of map features and their spatial extents.

Cartographers should avoid overprinting underlying graphics, which is to place a label on top of a map feature.

Point Features


When labeling geographic features represented as points on the map, there are a series of steps or guides that can be used. Be wise when following the guidelines and take into consideration that the first goal is to make a map understandable.


 * The preferred location of a label is to the upper right of the point feature, the second preferred location is in the lower right side, the third and fourth best options are to the upper or lower left respectively. When necessary, the labels can be placed either on top or below the point symbol. The least desirable positions are directly to the left or directly to the right of the symbol.
 * No other map feature should come between the point and its label. It is also important to place the point and its label close to each other to emphasize the association between the two.
 * When necessary, use leader lines to connect the point and the label. In most cases, the lines should not touch the point, the line should be thin and the use of an arrowhead should be avoided. If those options are not suitable for a given task, the use of a callout, a halo or a mask are encouraged.
 * Multiple line labels should be centered and placed in the preferred location of point labels.
 * Multiple lines of type should be centered or horizontally aligned according to the given scenario.
 * When mapping coastal areas, labels whose points fall on the land should also be placed on the land. Points falling between the land and the water must be labeled entirely on the land or entirely on the water.

Line Features

 * The labels for line features should be placed above the line.
 * For long lines place multiple labels; don’t spread text out.
 * It is possible to select from a number of different placement positions, offset types, and distances when placing labels for line features. Also controlling whether labels must be placed exactly at the location specified by the set placement parameters or whether they may vary within a given distance from that position. There are several combinations of label positions. They are the following:
 * Centered—Places the label on the feature at the midpoint of the label
 * Offset—Places the label at a default or user-defined distance or distance range from the line feature's symbol
 * Horizontal—Places the label horizontally relative to the upper and lower map border
 * Straight—Places the label on a straight line tangent to the feature
 * Curved—Places the label along the curve of the line feature or allow the label to conform to the line pattern. Similar to a river (e.g. geographic features), the label should flow around the edges along the line being careful not to have the letters too extended.
 * Perpendicular—Places the label perpendicular to a straight line tangent to the line feature


 * Water features, such as rivers, are labeled with Italic (slanted) letters. The names can be repeated at intervals, if necessary. The direction of the slant of italic letters should be in the direction of the flow if possible.


 * Linear features such as roads and railroads are labeled in upright rather than slanted text.

Area (Polygon) Features
Area labels should be positioned in a way that helps indicate the extent of the area that is being labeled. When labeling area or polygon features there are a few rules to follow.
 * Text should be spread out to cover the whole polygon. This allows for the visual of that entire polygon to be associated with the proper label.
 * The label should have margins on either side that are equal to the character spaces.
 * Uppercase letters are better when using character spacing so area labels often should be in all capitals.
 * Avoid placing labels outside the polygon; rotate text as needed. If the polygon is odd shaped or longer vertical rather than horizontal, rotate the text or curve it to fit within the polygon.
 * There is always the chance that the polygon is just too small for the label to fit inside. If this occurs, one option is to place the label on the map as if it were a point feature. The guidelines of labeling a point feature are stated above. Another option is to allow the label to extend beyond the boundaries of the polygon but place the label in such a way that it is clear which polygon it is labeling. The label must not hide or distort important features.
 * Avoid having several horizontally aligned labels because this makes them appear like a sentence.
 * It is important to make sure that none of the letters are placed in such a way that they appear as part of a map feature or line. For example, the letter "I" can appear to be part of a line.
 * In case of large water bodies such as lakes and sea, the shoreline should not be broken.

Label Management in Cartographic Technology
The software that is commonly used to create maps, including both geographic information systems and graphic design programs, provide a number of options for creating, editing, and storing the hundreds or even thousands of labels in a map. Each of these has advantages and disadvantages for particular situations.

Automatic Label Placement
This is an operation in GIS that automatically adds text to features on digital maps. For example, in ArcGIS software, there is an extension called Maplex that is used for this process. Automatic Label Placement can be a memory-intensive process, but can drastically reduce the time-consuming task of manually labeling each feature individually. Because it is an automated process based on algorithms, it can sometimes have undesired results. It is important to be aware though, that in some systems the text is generated on the fly every time the data is drawn. This means that each time the map view is adjusted the text labels are regenerated.

Labeling in Dynamic Maps
Dynamic maps are characterized by support for continuous change of scale (zoom) and continuous pan (change of region of interest), therefore, labels in dynamic maps must be placed at interactive speed. Statistic solutions for these types of maps are inadequate due to the orders of magnitude that need to be used.

Stored Annotation
In ArcGIS, there are two primary options when it comes to storing annotations: a map document or a geodatabase. If the annotations are stored in a geodatabase, they will be stored in what is called "annotation feature classes". If there are a few hundred pieces of text being dealt with, storing them in a geodatabase is best. Working with these annotations in ArcMap will generally be faster and can be applied to multiple maps. Annotations stored in a map document can only save that text in one specific map in comparison. Map document annotations also divide the data into annotation groups, depending on the data frame. Thus, the type of text (or storage) that is used will be dependent on how the text is used in the project. ArcGIS has created a table that can help determine how to perform the desired task depending on whether a geodatabase annotation or a map document annotation is used.