[gis_info] FW: Looking for advice on making an updating choropleth

[Darrell Fuhriman]

I don’t think there are perfect solutions to this problem, just less bad ones. The reality is if you’re looking at an exponential growth situation, this is bound to happen. This was exactly the problem that led to the argument a few weeks back about Georgia and its COVID case maps changing the scale — people thought they were being misled.

With the surge in COVID cases, the NYT recently had to change the scale on its maps, and they had a big caveat to that effect when they did.

I think that’s probably the least bad solution: update it the scale, but only occasionally. Make sure there’s a note right next to the legend that explains when and why the scale has changed. You could do it on an as-needed basis (but build yourself some headroom so it’s not happening weekly), or on a schedule, like quarterly or annually.

It’s probably also helpful to use a system where the bins are consistent, like a linear scale, and you’re just changing the top end of the scale. In other words avoid Jenks, which could just compound the confusion if someone is looking back at past maps, IMO.

Darrell
On Dec 3, 2020, 09:29 -0800, SMITH Cy * DAS via gis_info <gis_info at omls.oregon.gov>, wrote:
> Hi folks, we have a question about making good choropleth maps.  See below.
>
> cy
>
> <image001.png>
> Cy Smith, GISP
> Enterprise Information Services
> Data Governance and Transparency|Geospatial Enterprise Office
> (503)378-6066, http://gis.oregon.gov
> “Ensuring user-friendly, reliable and secure state technology systems that serve Oregonians.”
>
>
> From: VARGAS Antonio R * DCBS <Antonio.R.Vargas at oregon.gov>
> Sent: Thursday, December 3, 2020 9:19 AM
> To: SMITH Cy * DAS <Cy.SMITH at oregon.gov>; TANNER Joshua * DAS <Joshua.TANNER at oregon.gov>
> Cc: JOHNSON Nathan * DCBS <Nathan.Johnson at oregon.gov>
> Subject: Looking for advice on making an updating choropleth
>
> Hello,
>
> I was wondering if you or someone on your team could provide some advice or a reference to best practices that might help with a project.
>
> I’ve been asked to make a choropleth to illustrate dollar amounts going to each Oregon county to illustrate the progress of a program. The issue I’m having is that leadership would like to update the choropleth with new data each week, and I’m not sure how to choose the color scale to accommodate that.
>
> By the end of its lifespan, the dollar amounts will be roughly an order of magnitude higher than at the start. So, when I choose a color scale with enough room at the high end to account for this in the future, basically every county in today’s map is assigned the lowest colors on the scale. One idea we had was to use a continuous color scale, though the colors still end up very similar.
>
> On the other hand, if I were to update the color scale each time the data is updated, so that the data fills the whole color range each time, I expect that the colors assigned to each county wouldn’t change much over time. I guess the map would look wholly the same each data update, just with the legend assigning different dollar amounts to each color.
>
> Any advice would be much appreciated.
>
> Kind regards,
>
> Antonio
>
> -----
>
> Antonio R. Vargas
> Research Analyst
> Division of Financial Regulation
> Oregon Dept. of Consumer and Business Services
> Office: 971.345.1106
>
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