The map to the left depicts a part of Catholic life most Catholics are not too familiar.
This is sadly because Catholics do not often study maps!
So what does it all mean, you ask? Well if you're Catholic, you know the church you go to is part of your local parish and you may think that your parish priest is your shepherd, so to speak. In actuality, your shepherd is your bishop. What's more, he is the shepherd over all the Christians within his territory - and this territory is called a diocese. Every diocese has a central church where the chair of the bishop resides. In the Bible, the chair is considered an image of authority (for example, see Matthew 23:1-3) so the location of the bishop's chair is of importance. Since the Latin word cathedra means chair, the church containing the bishop's chair is called the cathedral.
Now looking at the map above, you'll notice that there are scores of dioceses in the United States. More importantly, you should also notice that some are placed into color-coded groups. These groups are called ecclesiastical provinces and they bear the name of the most important diocese within them. In fact, these dioceses are so important that they are each called an archdiocese and the bishop of the archdiocese is called an archbishop. The archbishop exercises a special unitive and leadership role within the province.
You may notice some black dots on the map above - and if you're looking even closer, you'll see that the color of the territory in which it is found is slightly discolored from the group of territories around it. This is because the discolored territory is the archdiocese of the province and the black dot locates for us the city in which the archbishop's cathedral may be located.
But there's more!
Present on the map are also seven red dots. These point out the cathedrals in the Archdioceses of Boston, New York, Philadelphia, Washington D.C., Chicago, Houston, and Los Angeles. What makes them so special is that their archbishops are also cardinals. Now a cardinal is a special title given typically to an archbishop of a predominantly Catholic area. In the United States, Catholics make up roughly 25% of the population - and if you don't know where they are mostly located, this map should help you! That said, the first thing you should notice is that the northeastern part of the U.S. is where you'll find a good deal of Catholics. But Chicago (remember the Irish and Italian mafia?) is also a heavily populated Catholic area. Demographics, however, are ever-changing and the steady flow of Catholic immigrants from Mexico is shifting the Catholic population further to the southwest. This shift made for a surprise back in 2007 when the Archbishop of Galveston-Houston was made a cardinal rather than the Archbishop of a midwestern/northeastern diocese (like Detroit, Milwaukee, or Baltimore). More expect this trend to continue and perhaps in the near future, Santa Fe and/or San Antonio could find themselves taking voting privileges from the northeast and bringing them to the southwest!
But why are cardinals so important? The answer is simple: they elect from themselves one who will become the Pope. If you recall, when Pope John Paul II passed the cardinals from all the countries of the world came to Rome and met in the Sistine Chapel where they elected Cardinal Ratzinger (who became Pope Benedict XVI). There are 120 cardinals eligible to vote in any given election - eligible because they are under the age of 80. If we count all the cardinals who are 80 or older, there are actually just over 200 cardinals. Here's one more interesting point: bishops are required to retire at age 75, but since a cardinal can still vote in papal elections for five more years, the archbishop who succeeds him is typically not made a cardinal for five years. On that note, I should point out that the red-colored dot representing New York is actually not currently led by a cardinal - but since Cardinal Egan (the retired Archbishop of New York) turns 80 on April 2, 2012, it is likely that Archbishop Dolan (the current Archbishop of New York and President of the U.S. Conference of Catholic Bishops) will be elevated by December, 2012.
This is of course simply the tip of the ice berg when it comes to the Catholic Church's hierarchy and territorial divisions - but hopefully you're ready to go read more maps!