From all the definitions of a Mind Map rooted in common experience I find representative the one based on the similarities to a city given by . A city is generally built around a centre (the central idea in Mind Maps) with boulevards (key ideas) branching in radial manner out of it, with secondary streets (secondary ideas) branching out of them, and gradually smaller and smaller streets (less correlated ideas to the central idea), and with cross streets (crossing ideas) connecting them. For a foreigner in a city it’s easier to memorize the boulevards and the streets toward the points of interest or relevance together with landmarks and images (e.g. buildings). Same as a tourist can manage in the territory with a mental map of the city, same a simple but well formed Mind Map can depict the essential structure of knowledge related to a certain subject. Actually a Mind Map could be compared with the Map of a city rather than the city itself, because both type of Maps represent the territory up to a certain level of detail, they are not the territory itself. On the other side the city like the Mind Map has a dynamic nature, while a Map is more static.
The example of a city has its flows – most of the cities have a networked rather than a radial structure, the number of dead ends could be significantly less than the streets ending in another street. In contrast a typical Mind Map has few crossing ideas, the dead ends governing its structure, for this reason the comparison between a Mind Map and a tree seems to be more natural. On the other side, the comparison with a city has other aspects – for example a city can grow forming a metropolis, same thing could be achieved by adding small Mind Maps to a central Mind Map. Two or more metropolis can form a megalopolis, each with its own centre or in contrast by developing their own centre or just gravitating around one of the already existing centres; the Mind Maps formed by the aggregation or two or more Maps are seldom, but not impossible to realize. Another example with small probability to happen is the one in which a city changes in time its centre, the old historical centre being replaced for example by a new business centre, reflecting city’s development; in the same way a Mind Map could shift in theory its centre, though this could happen more because of inconsistencies in Map’s building or because of changes supervened in Map’s detail. These characteristics of a city add a plus to this example versus the one of a tree, in which the trunk represents the central idea, the main branches the key ideas, and the decreasing in thickness branches the less correlated ideas. Unlike a city, a tree doesn’t include crossing ideas unless its 3-dimensionality is ignored or we deal with a curiosity of nature, the same applying to trees’ merging.
Trees have been used from Antiquity in order to represent knowledge - Trees of Life, Trees of Love, Trees of Knowledge, genealogic, kinship or blood relation trees have resisted the time on artefacts dated before B.C., or in printed manuscripts and documents especially from 10th century on, the richness of design and content increasing with the advancement in printing technology. The “Tree of blood relations” (fr: Arbre de consanguinité) appearing in Christiane Klapisch-Zuber’s book, L’ombre des Ancêtres is dated as belonging to the 9th century , several others similar trees are dated between 10th and 14th century and available online through Enluminures , or in the works of Joachim of Fiore , Ramon Lull  and others. Usually in such tree-like representations, the branches are just connectors between the various islands of text often represented as leaves, having the characteristics of archaic Mind Maps, resembling more to the graph-like representations. It is impressive the richness of styles and representations, the mixture between text and images, the use of colour and symmetric arrangement.
The city or tree syntagmas are just helpers in understanding the Mind Map, for a deeper apprehension of the subject is maybe more indicated to check Tony Buzan’s books.
 Enluminures. [Online] Available from: www.enluminures.culture.fr (Accessed: 1 October 2009)
 International Center for Joachimist Studies. (????). Joachim of Fiore. [Online] Available from: http://www.centrostudigioachimiti.it/Gioacchino/GF_Tavoleeng.asp (Accessed: 13 February 2009)
 MindMapping.com. (2008) Theory behind Mind Maps [Online] Available from: http://www.mindmapping.com/Theory_Behind_Mind_Maps.htm (Accessed: 1 October 2009)
 Weigel. S. (2002) Genealogy: On the iconography and rhetorics of an epistemological topos. [Online] Available from: (Accessed: 1 October 2009)
 Wikipedia. 2009. Ramon Llull. [Online] Available from: http://commons.wikimedia.org/wiki/Category:Ramon_Llull (Accessed: 1 October 2009)