Live data from Hacker News

Show HN: Play with an interactive heatmap of SF crime (and other cities)

safemap.io

41–50 of 137 posts

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#41

You need to divide crime counts by population density. Otherwise you're just plotting population density.

It's an important truth that walking a mile in a high population density area puts you at a higher crime risk than walking a mile in a medium or low population density area.

The population density in Singapore is much higher than in Detroit. Guess where you are more likely to become the victim of a crime..

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#43

Earlier quoted context omitted.

Thanks for checking out the site and for the feedback. It's definitely something we're looking into. It's kind of an interesting question though because it somewhat varies by crime category. Take car break ins, for instance - this is more of a constant factor than a population density scalar because the number of parking spots is generally fixed on a per-block basis rather than scaling with population density. I thin…

Parking turnover probably scales with population density. One of the reasons parking is more expensive in big cities is to encourage people to move their cars sooner. Smaller cities will have more cars that never move, where larger ones will have fewer.

If it's about movement, then population density might not be the best factor either. You might need some other way to see the number of humans moving through a given area. Stuff like office buildings have higher populations during office hours, but wouldn't be caught in "population" metrics.

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#45

Thanks for making this, it would be helpful if the city boundaries weren't so closely observed, most people don't care where the exact city lines are but have more of a feeling for the general metropolitan area as a blob

I wish that too but it seems their data sources are the cities themselves so those cities don't report things outside their jurisdiction.

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#47

You need to divide crime counts by population density. Otherwise you're just plotting population density.

Yes and no.

Not dividing by population density ~ Probability I will become a crime victim by travelling through that area

Dividing by population densitiy ~ Probability that I would be a crime victim if I live in that area

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#48
post #46

The location of the police stations seems influential. I know in Berkeley crimes without a firm location get geocoded to police HQ. Do you think that might be affecting these maps?

Interesting, thanks for the info. I think it hopefully should be OK for the currently supported cities. Lots of cities have 0,0 as the geo point for crimes without points, which we filter out. For others such as SF, it looks like the police HQ is in Mission Bay which doesn't seem to have a high crime rate for any category. This info would also hopefully be included in the dataset disclaimers, and we didn't see this in any of the datasets we use.

But thanks for the info, this is great to know for any potential future expansions. If you see any cases where this might be happening for the currently supported cities, please don't hesitate to get into contact with us :)

Re: Show HN: Play with an interactive heatmap of SF crime (and other cities)

#49

You need to divide crime counts by population density. Otherwise you're just plotting population density.

Thanks for checking out the site and for the feedback. It's definitely something we're looking into. It's kind of an interesting question though because it somewhat varies by crime category. Take car break ins, for instance - this is more of a constant factor than a population density scalar because the number of parking spots is generally fixed on a per-block basis rather than scaling with population density. I thin…

The number of parking spots may be static, but the number of potential thieves scales with population density.
Post reply on HN