Baltimore phenomenon

The “Baltimore Phenomenon”
The “Baltimore Phenomenon” is a cartographic term used to describe the tendency for a city to be omitted from a map due to space constraints while much smaller cities are included on the same map simply because space is available to display them. The term is named after the fact that despite its large population, Baltimore, Maryland, is commonly omitted due to lack of space available in the surrounding area of the map. Larger cities surrounding Baltimore take precedence. In contrast, much smaller cities in other geographic locations are included on maps of the same scale because the level of competition for map space may not exist in that particular area.
Competition for Limited Map Space
During the design process of any map, either created manually or electronically, there will always be a finite amount of map space and an almost infinite amount of information that can be included in that space. Voids in the map will be present in rural areas where population is not very dense. This creates an easier decision-making process for the cartographer since most cities can be shown. There is plenty of space and therefore very little competition for that space by objects or points to be displayed. In contrast, densely populated areas create the constraint of working with a limited spatial area for both points representing cities and the labels of those cities being displayed. Baltimore is the largest city in Maryland, but due to “its close proximity to Washington, D.C., and the necessity of labeling the oddly-shaped state of Maryland”, it is omitted on maps in favor of other places that fit more easily in the map space available. Unfortunately, Baltimore, despite its population, is omitted because of the necessary “competition for limited map space” in that geographic area. To illustrate this point, compare a map of the state of Maryland and surrounding area to a map of the state of Iowa and surrounding area. The entire population of Iowa is only slightly higher than that of Baltimore. When more space is available, many cities much smaller than Baltimore can be displayed.
It is notable that the Baltimore Phenomenon does not hold consistently true for every automated mapping site at every scale. Google Maps will display Baltimore once zoomed into the 7th zoom level. At the 6th zoom level, Baltimore is not displayed but cities such as Annapolis, Maryland and Newton, Iowa are displayed. Yahoo Maps displays the major roads surrounding Balitmore at the 6th zoom level, but no city label appears until the 7th zoom level. At this same zoom level on Yahoo Maps, cities such as Norfolk, Nebraska and Ottumwa, Iowa are included. Bing Maps displays Baltimore beginning at the 5th zoom level, but other cities and surrounding details at this level are fairly sparse. At this zoom level, Bing displays and labels only the largest two or three cities in the midwest area of Iowa and Nebraska. OpenStreetMap is similar to Bing in that it displays Baltimore more readily than Google or Yahoo, but midwest cities in Iowa and Nebraska at this scale are not labeled at all.
Cartographic Generalization
All maps are generalized representations of the actual geographic space. Cartographic generalization is a process in which geographic features are evaluated during a selection and simplification process. It is during this process that the cartographer or cartographic computer program decides what information should be included, how detailed that information should be and what information must be omitted. Boundary lines are smoothed and simplified, cities and towns are categorized and chosen according to relative size and importance, and comparisons of map features are made to determine what fits and what does not fit in the given map space.
Constraints, or guidelines, are put into place during the generalization process to help the cartographer achieve a high level of usability. Cartographers can control the map user’s interpretation of a map through manipulation and final display of the data being portrayed. The clearer the information and the more legible the map is, the better experience the map user will have and the more efficiently that map will convey the intended information.
The Selection Process
Many decisions made during the generalization process are not isolated from one another, and in many cases, manipulation of one cartographic aspect necessitates manipulation of other cartographic aspects. Multiple design decisions are typically made simultaneously by the cartographer and hopefully lead to the “most desirable degree of generalization”. Map design must always take into account that the human brain is only capable of taking in a finite amount of information at one given point in time. Keeping this in mind may help the cartographer enhance the readability of a map by limiting the amount of information on a map but it also puts restraints on the cartographic design and selection process.
Determining the Importance of a Place
In the selection process, many factors can be considered for rating the importance of a place. For generations, cartographers have chosen to base the inclusion of a town or city on that place’s relative importance. The importance of a place can be defined by many factors, but the most commonly used is size/population. “Size of population,” “administrative status,” “industrial plants,” “commercial and financial activity,” and “agricultural activity” are only a few factors to take into consideration. Highly-populated areas of a map can quickly become overcrowded when considering so many factors in ranking a city’s importance. In the case of Baltimore, size is not the most important selection criteria being used since Baltimore is the most highly populated city in Maryland, and yet the map of Maryland in the example above displays smaller surrounding cities. This reiterates the idea that the Baltimore Phenomenon is an issue based exclusively on spatial competition on the map.

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