A model is a representation of some "thing" (a situation, a phenomenon, an object, a collection of objects, ...) that is used instead of this thing:

portion of REALITY
(situation, object, phenomenon, ...)
that you want to observe
of the portion of reality

  a scale reproduction instead of the original figure,
  the grammar rule "the plural of nouns is formed by adding an -s to the singular" instead of the list: "abbreviation abbreviations, accent accents, …",
  compare different regions using population density instead of number of inhabitants and square kilometers of surface,
  the reconstruction of the factors that were at the origin of a certain event of antiquity and its description that are made by a history manual.

    The models are simplified representations that can facilitate communication, reasoning, …, but that can neglect or deform aspects that are present in the original thing and that must be interpreted taking into account their limitations:

  the cartographic reproductions do not faithfully represent the distances (see the figure at the side),
  grammar rules lose "exceptions",
  population density does not show how large the region is or how many inhabitants there are,
  the interpretation that a historian gives to the information available on a certain event is subjective and may differ from that of another historian.



    Let's see some other examples.

  Percentages facilitate the comparison between the parts that make up a total, between a part and the total, … , but, in return, they lose other information. For example, the incidence of beef on the total meat consumed per capita from 1926 to 1985 goes from 47% to 32%, but this does not mean that the consumption of beef decreases: if absolute data (i.e. not related to the total consumption of meat) it is observed that the per capita consumption of 10.1 kg per year passes to that of 25.1 kg per year; if a certain data increases but, in the meantime, also increases the total, the percentage that it represents can decrease.

  Average consumption and average height are average values in the sense that, with a single number, they give us an idea of the level of consumption oran idea df the heights of a population. However, they do not take into account the differences between individuals and individuals , which can sometimes be remarkable: behind a per capita consumption of 70 g of meat per day there may be those who almost never eat it and those who consume a few pounds a day.

  The average speed with which a means of transport has traveled a certain route is also an average value: it gives us an idea of how the means of transport traveled without a detailed description of how the speed has varied in the different stretches of road; it is the constant speed at which the vehicle should travel to take the same overall time.