Enabling interactive maps through transparency, layering and images
Confession time. This post has actually been six months in the making and the original idea came from my ‘Rainforest of the seas’ IronViz feeder entry. In this viz I used a Jonni Walker technique to layer a transparent image over the top of a map to effectively frame the map. It resulted in a square map appearing circular and being surrounded by splash marks. The visual effect was pretty cool but the big downside was the map no longer being interactive due to the image being layered on top of the map.
That was back in August 2018 and the dark days before transparent sheets. Oh, how times have changed!
Transparent sheets solved this challenge. They enable us to layer maps and images but also to add an additional transparent map on top which allows for the framed map to be interactive. I shall explain how to achieve this functionality through the example of my ‘Volcanoes Of The World’ visualisation:
The following steps were possible prior to 2018.3
Start with a base map
First, I created a base map; a map to visualise my chosen data but one that will only be used to display the background map layer, as opposed to any data points:
- Drop your longitude and latitude onto the sheet and apply your preferred map layer, in my Volcanoes viz example I used a custom MapBox background map but in reality you could choose any map layer.
- Hide the title.
- ‘Fix’ the map position to ensure the map doesn’t change when you filter the content.
- Remove map options to ensure no menu options appear on the base map.
Place this base map onto your viz, in your required position for where you want the map to appear.
Overlay a transparent image (PNG)
In the case of my Volcanoes viz I wanted to make the maps circular. To achieve this, I created an image in PowerPoint (Kevin Flerlage explains how to do this far better than I ever could), ensuring only the middle, circular, element of the image is transparent. Save the image as a PNG file and then place this onto your viz. My map was square in shape so simply overlay the circle using the same X,Y co-ordinates and the same height and width as the map.
The following steps have only been possible since 2018.3 and transparent sheets
Duplicate the base map but remove any map layers
Here is where the magic happens! Duplicate your original base map and amend it:
- Remove all map layers. A little tip here courtesy of @PromatixBI, if ‘States/Province Names is greyed out and you cannot remove it, you need to zoom in to a sufficient level, remove it and then reapply the same zoom as your base map. Thanks Chris!
- Remove map options.
- Edit your base map to set the marks card to 100 opacity; this will ensure only your duplicate map has visible marks.
Once you have created your duplicate map, place it onto your viz and set the shading of the Pane to none. This will give your duplicate map a transparent effect with the marks still being visible. Size and position your duplicate map using the exact X,Y, height and width options as your base map and hey presto, customised maps that remain interactive!
If ever you need to amend any element of your map, just ensure you do it for both the base and duplicate maps and remember to check the final order of your 3 objects:
- Base map: Furthest back
- Transparent image: Next
- Duplicate transparent map: Further forward
To view my ‘Volcanoes Of The World’ viz please click here.