Dolores Park on Sunday is perfect. The beautiful sunshine, the gorgeous view to the downtown, the newly completed children playground swarming with running kids. Everyone is having a blast. What a lovely day it is!

Dolores park (Jamison Wieser)

The only issue, ouch! Barely an hour under the sun is enough to get me sunburn. I know. I should have put on sunscreen. I have a tube with me but I just didn't expect such short exposure will do me any harm. This is a mistake I would have made many times.

But where is the San Francisco fog? The weather condition that the city is so well known for? A city shrouded in dense and cool fog. Foghorn blows the deep and the ghostly sight of cargo ship slowly emerge from the mist. The reputation of San Francisco fog spread so far that sometime visitors would ask for advice to plan around fog. How should they prepare themselves in the foggy weather. Bring umbrella? Trench coat? This is good for building up film noir atmosphere, but what you need in San Francisco is actually sunglasses and sunscreen.

As it turns out, San Francisco is one of the most sunny city in United States. It is not my wishful thinking. It is sunny according to meteorologists' statistics. 160 sunny days a year put it among the top most sunny cities. It even ranks favorably to the sunshine state of Florida, which is actually rather cloudy.

But what about the fog that engulf the city so often? It is of course no illusion. We residents experience it regularly. People who knows about San Francisco may point out to the effect of microclimate. Areas close to each other may experience dramatically different climate due to different geographic features like hills and valley. In general it means the coastal side is far more foggy than the bay side. To a visitor, it means Golden Gate Bridge and Golden Gate Park can be quite foggy, while Union Square, Embarcadero and the gorgeous Dolores Park are a lot less susceptible.

The microclimate explains some of the paradox. But what if I say the west side is also rather sunny? You may laugh at me really hard for saying this. That's pretty much people's response when the city of San Francisco announce plan to build a major solar power system on top of the Sunset Reservoir a few years ago. Everyone knows it is foggy in the Sunset district. To build a solar system there sounds so absurd that it is widely ridiculed. But wouldn't a professional solar developer have better idea then people who make judgment base on gut feeling? Indeed fog does not come all day to Sunset and it does get quite a bit of sun. According to the developer Recurrent Energy, the solar resource in Sunset is on average only 15% lower than the sunniest areas of the City and is consider quite good. With this solar power installation, it more than triple the energy San Francisco generate from the sun.

Sunset Reservoir Solar System (Recurrent Energy)

To make sense of the fog city so sunny paradox, it helps to understand a common bias known as base rate fallacy. Scientists find that people have a tendency, when making judgments of the probability with which an event will occur, to ignore the base rate and to concentrate on other specific information. Overall fog is a rather infrequent phenomenon. But the specific attribute of San Francisco's fogginess affect people's judgment more than the general base rate. To give another example, if city A hails 30 times a year, you will be right to consider it far more prone to hail than other cities. So how likely is it going to hail next Monday? Some people maybe tricked to think it is quite likely. They ignored the fact that hail is a rare phenomenon and even hail prone city A has 326 hail free days.

Let's not get distracted. Meteorologists say San Francisco is a sunny city. Bring sunglasses and sunscreen to enjoy your the visit. Don't get sunburnt like me.

2012.05.07 [San Francisco] - comments

The Doyle Drive demolition starts on Friday night. By Sunday morning the old viaduct is already reduced to toppled piles. The replacement Presidio parkway looks great by the way.

2012.04.29 [San Francisco] - comments

I just realize the chart I have made for on the census data of San Francisco's children was done badly. Here is my second trial. I thing this should be more clear. The key take away is San Francisco lost a big percentage of children in the 0-5 group after 5 years, but not so much on the older age group.

2012.03.09 [San Francisco] - comments

(Sorry these charts below are confusing. Please see the new charts of my second attempt.)

San Francisco is losing children population. Family move out of the city because of bad schools and expensive housing. Such is the popular conception of the issue of living in the city. But I have also heard some contradicting figures, like the kindergarten enrollment is steadily increasing in recent years. So rather than listening only to anecdotes, I am most interested in looking for some hard data to understand the extent of the issue.

Luckily we have the wonderful U.S. Census Bureau. They have collected and published lots of data at great level of details. Not only is the census of 1990, 2000 and 2010 available, the American Community Survey has also provided 1-Year estimates for every year since 2000. This allows me to do an analysis on the demographics. By tracking individual cohort and comparing their population change over time, it is able isolate other factors to provide insight on whether or how children leave the city.

The analysis mostly validate the observation that children are leaving the city before entering school. Moreover it suggests that the initial elementary school enrollment is the only event that triggers mass migration. Other factors, like real estate concerns, may not play any significant role.

First of all the overall population of San Francisco is growing slowly. It has recovered from the lost after the dot-com crash and arrive a near all time high 0f 800,000. This is 11% over the population of 1990.

The children population, in this study it is defined as 0-19 year old, has shown similar fluctuation around the dot-com crash. However the overall trend is slightly down, it is 2% less than 2000 and 6% less than 1990. Since the overall population is up, as the percentage of population the decline is even more steep.

Looking at the population of the group from new born to 4, it has instilled some hope. The number is holding up well and perhaps even on a upward tread. The number is slightly less than 1990 but 11% more than 2000.

The next 2 charts are perhaps the most interesting in this analysis. Rather than looking at one aggregated number, we track the individual cohorts and compare its change in 5 years. This directly answers the question whether children are leaving San Francisco. For example, the blue data point at the lower right hand corner represent the group of 0-4 years in 2005. It says that in 2010, when this cohort turns 5-9, their population is only 72% compare to where they have started. One quarter of them has left due to net migration. The green data point at the upper right hand corner tells a more positive story. It says that the 10-14 cohort in 2005 gains 20% in 5 years when they have turned 15-19 in 2010. Older children are actually moving into the city.

The population in separated in three groups (as compiled by the census bureau), under 5, 5-9 and 10-14. They shows a rather divergent outcome. Nearly all the losses come from the under 5 group. And it is at a rather significant drop of one quarter in size! The lost ease up for the older group. In fact more recent census shows that the cohort actually grow in size!

(One note about the five year change charts, the child mortality rate is negligible here. The changes mainly come from net migration.)

While it is a good for population to grow due to immigration, we are particularly interested to see how well we are retaining children who are already in the city. For this we compare the population of each cohort as a percentage of population instead. The overall pattern remains similar, although it makes the lost of the under 5 group even more terrible. This metrics maybe a little bias against the children population though, because I believe the recent influx of immigrant is more likely to have a higher percentage of childless adult as they are more mobile.

The sharp drop of children after they turn 5 points to one single issue, family are leaving at the time when the child first enroll in school. People are concern about the quality of public schools. The assignment system leave them feel out of control. Many bait out when they are not assigned to popular schools.

A sharp drop of children at age of 5 is a more acute problem than if the drop is gradual over time. It lowers the basis for the older groups. Even when there are population increase in older group, it is already on a smaller base. And it comes too late to make a long term boost to the children population.

On the other hand, this analysis largely discount other issues such as housing problem. As children grow, they need more space as they grow physically bigger, acquired more stuff and become more independent. The housing issue should have become more pressing over time. However the population drop off ceased and it even turned into growth for older groups. Housing issues seems far less influential compare to school enrollment.

To halt the exodus of family, the key is in improving the initial school enrollment. As a parent who are right at this watershed stage, I find the public school quality issue is often a perceived one. Nearly all the schools I have toured leave me a positive impression. And those are not even trophy schools people are clamoring, but simply neighborhood schools. It is unfortunately to find so many people dismiss the schools as unacceptable before even trying.

Here is the data I have prepared for anyone who want to validate or further analyze the result.

2011.06.23 [San Francisco] - comments

Here are the pictures from last week's Sunday Streets. Somehow this is only the first time I attend the event in my own neighborhood. What a great afternoon it was.

2011.06.22 [San Francisco] - comments

SFUSD has released the Round 1 Demand data for the 2010-2011 school year. The data is in PDF format, making it rather hard to do any analysis. For the benefit for myself and others I've converted the K-level data to spreadsheet format. For example, I used the data to generate the over/under-subscription chart below. I subtracted the number of first choice requests from the capacity to come up with the absolute over-subscription number.

It also shows that the top 10 school programs account for 72% of total number of over-subscription. Two third of the programs are balanced or under subscripted with respect to the number first choice. This includes the popular West Portal GE! It seems not that hard to find some good school with good confidence to get in. Of course the Diversity Index system makes everything unpredictable.

2010.03.15 [San Francisco] - comments

SF Appeal has published the Muni onboard video recording of the collision between a Muni #19 bus and a pickup truck on Jan 5th morning. The intersection is controlled by four way stop sign. Question has been brought about who's at fault. I have reviewed the video frame by frame. I come to a clear conclusion that the truck driver was at fault. While the bus driver technically did not made a complete stop, it has the right of way. The accident was caused by the truck running the stop sign at a high speed.

The four frames below captured the action during a span of 2.8 s until the moment they collided.

• Frame 1 - 00:02:34.22
• Frame 2 - 00:02:35.02
• Frame 3 - 00:02:36.02
• Frame 4 - 00:02:37.02

At frame 1, using the trash can as a reference point, it shows the bus was right at the intersection. The truck was about half a block away. It should be immediately obvious that the bus has the right of way.

At frame 2, the bus rolled forward. The truck was still some distance away.

At frame 3, the bus proceeded across the intersection slowly. The truck still have not arrive at the intersection. It should stop and yield to the bus.

At frame 4, truck ran the stop sign at high speed and caused the collision.

Base on the video frames, I plotted the estimated position and the movement of the vehicles during this 2.8 s on a map. I estimated the bus has rolled through the stop at 8 mph. In contrast, the truck has flown through the intersection from half a block away at 32 mph.

The verdict is clear, the truck driver was driving recklessly and caused the accident.

San Francisco Chronicle has published an article with the release video titled "Crash video shows bus, pickup ran stop signs". It implies they are equally at fault. I think this is wholly a mischaracterization by failing to unambiguously call out it was the truck's fault. The bus had the right of way. Actually had the bus made a complete stop the same accident could still happen.

2010.01.07 [San Francisco] - comments

Last Saturday I have joined WalkSF in their annual Peak to Peak Walk. We gathered the starting point at West Portal. It was sunny when I took off from the east side. Who would have expected it was actually drizzling in West Portal! We headed out to the wood in Mount Davidson and then Twin Peaks and over a series of hills in San Francisco. When we have arrived on Twin Peaks, we were right at the edge of the morning fog. The scenery change from instance to instance. One moment we saw the Sutro Tower floating in the air, a moment later it was hidden by fog. I find such scenery magical. I have also visited the beautiful campus of USF for the first time. The walk ended in Coit tower where we have a small picnic.

I was also using this walk as a training opportunity for my upcoming trekking trip in Peru. I carried a backpack with 20 pounds weight the entire day. I don't know if this is a significant factor, but I was really tired at the end of the day.

2009.10.27 [travel, San Francisco] - comments

Yesterday the car free event Sunday Streets was held in Mission. A section of 24th St and Valencia St were closed to traffic so that people can come to the street to play. Since I live nearby, I just rolled down the hill on my bike to check it out and then have lunch and go for a movie. [more...]

2009.06.08 [San Francisco] - comments

While I have ridden my most favorite Golden Gate Bridge bicycle route great many times, today I have extended my range to the Larkspur ferry terminal. What promoted me to go is because bicyclists are offered free ride on the ferry in the weekends of May. This gives me a great excuse to explore the part of Marin County that I have not been to before. It delights me to find a bike path that goes nearly all the way from the Golden Gate Bridge to Corte Madera. The path goes through the mud flats along the bay. While it is not as spectacular as the Golden Gate Bridge, it offers me a quiet and nice diversion. [more...]

2009.05.23 [San Francisco] - comments

KFOG put up their kaboom fireworks show last night by Embarcadero. I always consider it the best fireworks of the year, trumping even the New Years Eve fireworks. This year I notice something interesting. The fireworks is reflect by the the newly raised glass tower of One Rincon Hill, making the tower itself a sparkling display. Too bad I can't get a good shot with my basic camera. [more...]

2009.05.10 [San Francisco] - comments

Two hospitals in my neighborhood both plan to build a helipad on their roof to transport patients. This draw some very vocal opposition in the neighborhood because they think it will give off terrible noise. UCSF has done the best thing by running a test flight this Sunday. I have taken a shaky video below. This is captured near the new children's playground on Arkansas St using a simple Canon A570 camera. [more...]

2007.10.22 [San Francisco] - comments

After all these years living in San Francisco, walking and biking the Golden Gate Bridge no less than 30 times, I have finally make it to Battery Spencer above the bridge. On the Marin end of the bridge I rode my bike up the sleep slope to get there. The reward is a most glorious view of Golden Gate Bridge and the bay. [more...]

2007.09.23 [San Francisco] - comments

On the new year's day I caught this view of Bay Bridge in fog. The fog cleared up in the afternoona and we had a great day's out. [more...]

2007.01.01 [San Francisco] - comments

The Chronicles has published this year's Bargain Bites restaurants. I think it would be so much better to put them on a map and see them at-a-glance. So I have made one myself using the Google Map. Check it out - the San Francisco bargain bites on google map.

2006.09.21 [San Francisco] - comments

Since it opens in 1930s, over a thousand people have taken their own life plunging into the cold dark water under the Golden Gate Bridge. Should a barrier be built to stop people from attempting suicide? That is the rebate reignited recently. My first reaction is if people cannot jump from the bridge, they will find another way to kill themselves. A barrier is likely to be costly, ugly and not necessary effective. Like many people I identify the bridge as an landmark icon but have certain sense of apathy and even regard this as a myth.

I have eventually changed my position. A barrier should be elected. Think about it. The Golden Gate Bridge really has a magical spell to be the place to end one's life. Once we stop making it convenient, most suicidal people are probably not as determine as we would have thought.

The Chronicle is running a 7-part series on the barrier issue. By taking a close look at the people involved it gives another dimension to the issue. These are wrenching and anguishing stories about real people, many of them young, brilliant and promising. Let this be a wake up call, for we have really ignored the issue for too long.

2005.11.02 [San Francisco] - comments

The news of San Francisco building a city-wide wireless network is getting a lot of attention these days. Broadbandreports runs several stories on this. While broadbandreports itself is a proponent of municipal broadband, I am surprise that the news draw torrents of criticism from readers. Many reject this because it is a 'liberal' thing. Other took the line of incumbent telcos that existing access methods is preferable to a public project.

While I think many posting are nothing but political fervent, I am also disappointed that people do not see the potential of universal connectivity as a big step forward (a departure from the usually 'hypish' technology sector). I have posted my reaction, which I include here:

---

Reader's post

Disgusting

It is pathetic how the flaming Left in this country has confused the term "right" and "entitlement." Sure, everyone has a "right" to Wifi. There is nothing stopping you from working, earning some money and buying the needed tools yourself. Its no different than there being a right to free speech and free press. Does this mean the government is required to provide you with the means to exercise those rights? Of course not.

Some other posters here have mentioned guns. Under Mayor Newsom's reasoning, the right to gun ownership requires that the government give free guns out to everyone.

---

My response

There is nothing stopping you from working, earning some money and buying the needed tools yourself.

True. There is also nothing to stop private entities to build railroads and toll roads and then charge everyone a use fee either. Just like what the country did a century ago. Do you find it disgusting that the government took it upon themselves to build roads and offer it for free to people?

Look there are no lack of proposals from commercial companies to offer the service, apparently costing the city little. People get access in the parks and schools and cafe and hopefully all pocket of households that do not yet have access. I don't understand what the objection is. Do you have a better proposal?

3G, if it is available at all, would cost a bundle. Imagine now that there is universal wireless access. You go to a shop and look at an item. You'll pull your PDA or cellphone and do a search on the UNC code. Immediately it turns out a list of reviews, links to other outlets, and recommendation for alternatives or accessories you'll need. You'd IM your wife. Once she sees the picture she'd told you you got the wrong stuff again! That's new commerce that will be enabled by universal access! You'd bet Google is working on that already!

You'd think broadband report readers are a bunch of smart guys. But when it comes to public project all the anti-government ideology would just overcome their judgement. Guys I'm off to hack the next big thing for the future of universal connectivity. Go on with your anti-government bashing.

2005.10.04 [mobile, network, San Francisco] - comments

If you have been to San Francisco downtown's Rasputin Music store you have probably taken the elevator, a closet-size box christened the Transporter Room, to go between floors. You would probably have pity on the operator, who spends hours sitting in that claustrophobic box. SFGate.com took an interest on them and run an interesting story today. In the elevator you might find painters, poets and other intellectuals as well as a trained librarian, and someone with a Ph.D., as well as aspiring musicians running it.

Believe it or not, among the store's steady stream of job applicants, there are always some people who want to apply just for that gig.

2004.09.01 [San Francisco] - comments