Media for Cellphone tower coverage Qs [Telecom]

Cellphone tower coverage Qs [Telecom]

Today's SF Chronicle COMPUTING column has some Q&As about cellphones and this URL was mentioned:

Curious, I wanted to see where the local cell towers were located for my carrier (AT&T Mobility grandfathered all the way back to Cellular One). I seldom have fewer than 4 (out of 5) bars on my phone's display, so I figured there would be a hive of towers especially here, Silicon Valley.

Visiting this URL:

and clicking "[*] AT&T", I wondered where the towers were and had to zoom out to see a few.

There's a cluster of 3 flanking Moffett Federal Airfield about 3.5-4 miles north from my home, another grouping of 5 about 8-9 miles east between Santa Clara and San Jose, then two NW about 20-25 miles away in Burlingame. That's it for the places I normally would be concerned about coverage.

This doesn't make any sense to me for two reasons:

I have excellent signal strength at my home, and
if I dial 911 (on the cellphone) from home I get the local city's 911 center, and if I dial 911 while driving along I-280 all the way up to San Mateo (just south of Burlingame) I get the CHP 911 dispatch.

My two questions:

is that tower spacing "normal"? The "cellreception" site claims to have all registered towers in its database of 135,800 towers last updated in May 2009.

how/why would I get routed to CHP's 911 while on I-280 headed NW even just a mile or two from home while I get routed to the local city's 911 if I call from home? [I'm not complaining because that's exactly what I want to happen]

The reason I'm puzzled is that when the service was still Cellular One they claimed a tower within 1/2 mile of my home and even assisted getting service to function within the local food supermarket which had a metal roof and zero reception. Later, as Cingular, again I was informed new towers were being installed. To date since AT&T acquired the contract, I've received no indication of new towers, only claims of "service improvements" -- given I really have no quarrel with AT&T Mobility, I accept that claim.

Perhaps I should be asking: is there a better resource showing cellphone coverage and/or tower locations by carrier?

I'm still scratching my head wondering how cellphone service works here at all. :-)