Each week I will be blogging about a different application of GIS that the general population can relate to. This week's post is going to talk about population accessibility, specifically related to emergency room visits. First off:
Access to Services and GIS? This is a classic application of GIS. Simply put, we can use geospatial technology to measure how populations may access services using travel networks. This is typically done by using shortest path or closest facility algorithms which I won't get into here. What we will get into is how to measure the impacts of moving a facility for an affected population.
The set up: The population of the City of Vancouver currently can conveniently access Six Emergency rooms in Metro Vancouver (I've discounted BC Children's Hospital so we can focus on population in general). From this I wanted to find out:
For each block in the City, where is the closest emergency room?
On average, how far do Vancouverites (all 602,000 of them in 2011) have to travel to get to an emergency room?
For whom in the City is Saint Paul's Hospital the closest ER facility?
How much more, or less, further do these folks have to travel should Saint Paul's move to its new location on False Creek?
Some additional assumptions:
This is a mini project so I only looked at home-to-emergency room trips via car. (ambulance dispatch is another project entirely);
Since February 6th is still a ways off, I used 2011 Census population data (specifically Census dissemination blocks);
All populations are treated equally in this little exercise. In reality, there are populations at risk who tend to use emergency services a lot more. I'm not looking at them right now; and
I am looking at distance traveled along roads only and not travel times, though I will likely add this in a later post. So, for the purposes of this post, we will use distance and time interchangeably (though in reality they couldn't be more different!
So how does Access change after the Saint Paul's Move? (play with the slider! the left side of the slider is the proposed state and the right side is the current state)
It may be a bit hard to see, but basically moving Saint Paul's hospital puts a lot more people into its catchment versus it's old location in the West End (Each colored line represents the minimum travel distance from a block to it's nearest ER). The relocation of Saint Paul's reduces potential use of Mount Saint Joseph by taking residents in the DTES and in Mount Pleasant (wait 'till we redo this analysis when the new Census comes out!), but increases potential usage of Vancouver general due to folks in Kitsilano staying on their side of false creek. Overall, it appears as if this balances potential ER usage. However... What about the change in distance to services after the Saint Paul's Move? This is where it gets a bit more interesting (and complicated). If we take population-weighted City-wide average it looks like average distance to a facility increases by 87m (from 3,132m to 3,219m) or about 2.7%. However, when we review distance traveled in summary by current catchments (ie categorizing the population based on the ER they are currently closest to), we are presented with a different picture. Take for instance what happens to populations currently accessing Saint Paul's in the West End:
You'll note that the travel times appear longer (more brown than yellow in the future state). While it is intuitively obvious, it's nice to have a visual that shows how many more people will be potentially travelling longer distances to get to emergency services (That being said, populations at risk will be much closer to the emergency room). Unfortunately, it is mostly residents of the West End and Kitsilano who may have longer commutes to the ER. Indeed, for the rest of the City things improve with the Saint Paul's move.
Refer to the table to the right: Essentially folks who are currently living in the Saint Paul's catchment (ie Saint Paul's is their closest ER), will have to travel, on average, an extra 1,047m to get to emergency services! Compare that with individuals who currently are in the Mount Saint Joseph catchment. Under the proposed change, some of this population will switch to the new False Creek location of Saint Paul's and, as such will have a shorter distance to travel (on average 318m less). Otherwise things are mostly a wash.
So, you've seen at this very superficial level how we can use GIS to explore how some populations may be inconvenienced by the hospital move. Now of course there are many, many more facets to the analysis. For instance:
what about emergency closing times;
wait times;
ambulance access;
travel times;
different modes (such as SkyTrain);
different population cohorts;
future populations;
daytime population; and
the list goes on.
The point is that I love doing these types of analyses. If you or your organization has the need to measure how population access will change when you move a facility then please contact me at aaron@lgeo.co and I will be happy to talk about your needs. In the meantime, I would love feedback on this post. Also if you want to learn more about the Saint Paul's relocation then please check out their website here. There is much to learn about this interesting project. Now, I will blogging about intriguing GIS weekly, so if you have an idea for interesting and challenging geospatial analysis, then I will work into my future publications. -Aaron