The arrondissements Paris' twenty districts
Paris is divided into twenty districts known as arrondissements. These numbered districts make up what's commonly known as "Zone One" of Paris. The arrondissements are arranged in a clockwise spiral pattern, starting dead center with the first arrondissement focused on the Châtelet – Les Halles area, then twirling out from there, so that the highest-numbered arrondissements (twelve through twenty) make up the outer edge of Zone One of Paris.
Each arrondissement is named simply by its number; the first district is le premier arrondissement (or le 1er arr. for short), the second is le deuxieme (or 2eme), and so forth. This is important to know because a lot of places in Paris are commonly identified by in which arrondissement they're located. You may meet someone who recommends a good restaurant, for example, and they'll describe its general location by saying, "It's in the fifth." This goes for people, too! Many Parisians identify with their arrondissement. A common topic for smalltalk in social situations is the question of what neighborhood one lives in (or is staying in), and most Parisians will answer, "I live in the eleventh," or the fourteenth, or whatever. Each arrondissement has a unique flavor and in some cases it may be a point of pride for someone to live in, say, the sixteenth because it's ritzy, or the eighteenth because it's artsy, or the fourth because it's the gayborhood. Once you get to know the personalities of the arrondissements, that simple number can tell you a bit about that bar you're considering for tonight or that store you wanted to check out.
When you're out and about in Paris, you can always identify which arrondissement you're in by looking at any street sign. The little blue-and-green metal street signs that are attached to buildings at every corner usually contain a little rounded tab above the street name that shows the number of the arrondissement you're in.
You can also easily figure out what arrondissement any Paris address is in by looking at the postal code. All Paris addresses within the twenty arrondissements consist of five digits, beginning with "750" and ending in the two digits of the arrondissement. So an address with a postal code of 75013 is in the thirteenth, and 75006 is in the sixth, etc. Get it? If it doesn't start with 75 then it's not in central Paris! Keep this in mind if you find a hotel deal that seems to good to be true. You may find hotel cheaper deals that involve a short train ride to get into the middle of where things are happening; this may be a good thing if you're looking to save money and don't mind a little extra time in the Métro or RER (regional train) every day! But in general, if you want to be in central Paris and relatively close to everything, you want to be in 7-5-0-something-something, and the smaller the number the closer to the center you are. See, easy!