About Ile de France and Paris
The region of lle-de-France (population 11 million), in northern central France, comprises eight departments. The city of Paris, a department unto itself (see below), is the heart and soul of the lle-de-France, which is sometimes referred to as the région Parisienne. The three departments immediately adjacent to Paris, which make up the so called petit couronne ('small crown' or 'small wreath') are Hauts-de-Seine (92), SeineSaint-Denis (93) and Val-de-Marne (94). The outer circle of departments is called the grand couronne (1arge crown' or 'large wreath') and consists of Seine-et-Marne (77), Yvelines (78), Essonne (91) and Val-d'Clise (95). lle-de France means 'island of France' and, although the region isn't literally an island, it's more or less surrounded by rivers and was therefore considered an island through much of French history.
The Ile-de-France covers 12,070km2 (around 4,700mi2), a little over 2 per cent of France's land mass, but houses over 15 per cent of France's population. (Those who live in the lle-de-France are called Franciliens or Franciliennes.) As these figures indicate, the lle-de-France is the most densely populated region in France, with an average of around 900 inhabitants per km2 overall. Paris is Europe's most crowded capital, with over 20,000 people per km2 (over 50,000 per mi2), almost five times the population density of London, compared with a mere 200 inhabitants per km2 (around 500 per mi2) in relatively rural Seine-et-Marne. Overall (and obviously there are wide variations), the region is 20 per cent woodland, 20 per cent grassland, 50 per cent arable land and 30 per cent other uses (including urban areas). 
The Ile-de-France is also, not surprisingly, the wealthiest region in the country in terms of the number of people with high incomes. Of the 100 main cities and towns in France, the Ile-de-France contains six of the seven wealthiest - Saint-Germain-en-Laye and Versailles (78), Boulogne-Billancourt, Neuilly-sur-Seine and Rueil-Malamison (92) and Paris itself (the other is Cannes in Alpes-Maritimes). Together, these are home to almost 37 per cent of the country's richest people (almost 17 per cent of French people liable to wealth tax live in Neuilly!).
The lle-de-France region offers a wide range of living environments and types of accommodation, as do the various districts (arrondissements) and neighbourhoods of the city of Paris. Each department and each district has a general character and reputation, although there are exceptions and 'atypical' towns and districts in each area.
Paris
The 'City of Light' is the most popular tourist destination in the world, having many of the world's great museums and galleries, as well as world renowned restaurants, cafés and bistrots, and enjoys a deserved reputation for fashion, romance and passion.
The city is divided into 20 arrondissements, each of which is a distinct political unit with its own town hall (mairie), mayor (maire) and police headquarters (préfecture) handling day-to-day administrative matters for local residents, including marriages, birth records, death certificates and voting. (The Mairie de Paris is an administrative centre for the 20 district governments and not normally open to the public.)
The numbering system for the arrondissements starts at the Palais du Louvre, formerly the French king's primary residence located roughly at the centre of the city, and proceeds in a clockwise spiral out to the city limits. Almost all addresses and directions in Paris include the relevant arrondissement number (as well as the name of the nearest underground station). For example, the post code 75016 indicates an address in the 16th arrondissement.
In an effort to lessen dependence on Paris, the government established five satellite towns in the mid-1960s, with the intention of making these 'new towns' (villes nouvelles) self-sufficient in terms of employment, local commerce and public services. The villes nouvelles are Cergy-Pontoise in Val-d'Oise to the north, Saint-Quentin-enYvelines to the west, Evry in Essonne to the south, and Marne-la-VaIIée and Sénart in Seine-et-Marne to the east. Although the experiment wasn't entirely successful, the villes nouvelles have managed to dilute the concentration of jobs, people and services in the capital to a certain extent and offer a less frenetic alternative to the urban intensity of Paris itself.
©Text by David Hampshire, from Survival Books' Buying a Home in France