Often times, you'll hear a city referred to as a "baseball town", "football town", "hockey town", or whatever sport that town happens to be a town of. A common example of this moniker would be St. Louis's designation as a "baseball town"; Bud Selig actually once referred to St. Louis as "the best baseball town".
So, what is San Diego? Can they be considered a town with a pre-dominant interest in one sport? While the Padres owner may say otherwise, I believe there is ample reason to believe that San Diego is a football town.
Some basic observations about San Diego
San Diego is rarely called a football town or a baseball town. In fact, a google search for "San Diego is a baseball town" and "San Diego is a football town" returns less than 3500 total results, compared to 96900 for the example "St. Louis is a baseball town" above. So to start, this isn't a topic that has been broached much with regards to San Diego. However, as the city's interest has clearly changed, as demonstrated below, I expect "San Diego is a football town" results to increase.
In San Diego, interest in the four major sports has significantly changed over the past decade. Google Trends only goes back until 2004, but a look at relative search interest in each of the four major sports from 2004 through the present shows a clear trend: interest in the NFL and NBA is rising, while interest in MLB is not.
You may be thinking: isn't that true for the United States as a whole? No, as you can see below. While NFL and NBA are certainly rising in the US, MLB is too. Also, take a look at the difference between the NFL and MLB in both charts. In the US as a whole, the NFL is searched for roughly three times as much as MLB. In San Diego, that ratio increases to roughly 4 to 1. (For reference, "baseball town" St. Louis is at less than 2 to 1.)
San Diego's declining interest in the Padres
The decline in baseball-related searches in San Diego can at least partially be attributed to the decrease in interest that San Diegans have in their hometown Padres.
The general decline
For the past seven seasons now, the search phrase "San Diego Chargers" has had a higher peak search popularity and higher average search popularity than the phrase "San Diego Padres". As you can see, though, it certainly wasn't always that way; the Padres have been in a steep, steady decline since 2004:
Additionally, the Padres are struggling to generate interest online in other ways. Their team site, Padres.com, hasn't ranked better than 20th in baseball in any month since 2009 (which is as far as the traffic site I'm using goes back in time); conversely, the Chargers team site ranked 14th last month. Similarly, the Padres SB Nation syndicate blog ranks dead last in views and unique visitors among SB Nation MLB syndicate blogs; conversely, Bolts from the Blue ranks in the early 20s (and is ascending). Only one day this entire baseball season saw the Padres SB Nation blog exceed the Chargers SB Nation blog: the day following the Grienke/Quentin brawl.
So how come searches for the Padres have declined?
The Padres have jettisoned their most popular players
One thing (besides the losing) that the Padres did in the past half-decade that, I believe, significantly contributed to the lack of interest in the team was getting rid of all their good/interesting players as if it was their sole purpose as a franchise. Nothing proves that better than the following Google Trends chart showing search popularity for various players within San Diego County:
The green chart there, apparent when hovering over it, includes basically all the players the Padres got back in the Peavy, Gonzalez (and subsequently Rizzo), and Latos deals combined into a single trendline. Disappointingly, excluding the term 'steroids' from this grouping (since it includes Yasmani Grandal and I assume steroids counts as negative publicity) further reduces the trendline popularity by 22%.
As you can see, the troughs in Peavy's search popularity during the end of his tenure in San Diego is basically the same as the peaks exhibited in the green combined trendline. With the exception of the past three months, even after Adrian was dealt, searches for "Adrian Gonzalez" in San Diego still surpassed combined searches for the green group.
The three most popular Padres in terms of search volume in San Diego are Carlos Quentin, Chase Headley, and Huston Street. Amazingly, during the Padres' 2012 season more people in San Diego searched for "Philip Rivers" than they did for "Chase Headley", "Carlos Quentin", and "Huston Street"...combined! This despite the Headley trade rumors, Headley's breakout second-half, Carlos Quentin's extension, and Huston Street's extension...AND it being the Chargers' offseason! See below:
While the Padres may like to wax poetic about being a team rather than a group of individuals, when it reaches the point that your billboard advertisement in San Diego's airport is of a face-less player, it's safe to say you've harmed your franchise's popularity.
Why San Diego's interest in the Chargers is likely to increase
In addition to the ascendancy of football-related search terms in general, there are reasons specific to the Chargers that lead me to believe that the trend will continue.
There's ample reason to believe that interest in the Chargers may increase in the near future: Norv Turner and A.J. Smith are (finally) gone. Don't believe that will stimulate an increase in interest in the team? Well, besides the anecdotal evidence that I will be attending several more games this season now that Norv is gone, we can once again consult Google Trends to examine Norv's (negative) popularity.
Incredibly, over the course of Norv Turner's tenure as Chargers' head coach (from February 2007 through December 2012), the search term "Fire Norv" has relatively the same search popularity as the Padres' manager for that entire duration: "Bud Black". Read that again: the exact phrase "Fire Norv" was basically as popular as the Padres' manager. The proof:
This is a remarkable indictment of how negatively the public viewed Norv Turner (and general disinterest in the Padres), leading me to believe that his dismissal was not only welcomed, but may lead to renewed interest in the team simply because he's no longer in charge. In other words: I'm postulating that Norv and A.J. Smith were suppressing fan enthusiasm for the Chargers.
In conclusion: a new era
Not only do I think getting rid of A.J. and Norv will bring back fans, I think the new regime has brought hope to a franchise that has had a steady decline over the past half-decade. In addition to bringing in a new system with documented success, the new regime has avoided the term "rebuild" in describing their direction for the team. A system with documented success and a regime avoiding rebuilds is about as opposite as it can get from the other San Diego franchise; which is a huge reason why San Diego, for the time-being, is a football town.