Should I use sliders to show differences between two maps?
My recent deep dive into usability has opened me up to the possibility — and likelihood — that my opinion is most likely completely wrong.
In a recent project, we were testing something that I felt wasn’t very helpful to users — sliders. This opinion was entirely my own. It wasn’t based on user observations or usability studies. I just thought that they weren’t helpful.
I was wrong.
In the project, I was conducting a usability study. I had no emotional attachment to the code, nor to the design. The project looked at how two variables change over time, and what the impacts of the change will be on the landscape.
To do this, the developers/designers used a slider that transitioned two images as the user dragged the slider bar — we see these a lot when people want to look at before and after satellite photos of natural disasters.
Here’s an example of a slider I created to show the difference between two National Land Cover Database (NLCD) Landcover datasets.
I’ve always felt that this was a little clumsy, and I worried that people would come to the wrong conclusion, although I had no alternative solution to offer.
For the usability task, we asked study participants to use the website and describe what changed between the two images provided — hopefully using the slider — at a location they cared about.
To my surprise, all participants used the sliders without issue, and accurately.
In the past, during other usability studies I’ve conducted, I’ve found that people typically struggle with this type of task. In this instance, though, it seemed that the sliders were doing what we had hoped for.
In fact, one participant started the session stating, “I really don’t like sliders — they don’t work. So I’m biased.” Then, in the middle of describing the change, that same person stopped and said, “Hey…wait a minute! I think these sliders might actually work. Especially when you’re zoomed in and focusing on a specific area.”
This brings me to a new view on using sliders to highlight differences between two images.
Before the study, I wouldn’t even have considered using sliders.
Now, I would most definitely use them in cases where we assume that the user will be doing a similar task — going to an area they care about, and trying to understand the differences between two images.
Next up? I really want to see how people deal with a side-by-side map to do the same task. Will a side-by-side map be more informal? Will they struggle? Which is better?
I can’t wait to get a chance to test this and share the results with you.
