I have a question about something which I think is possible but just can't get my head round it, and haven't found any answers online. I'm using $id= @atlas_featureid in QGIS 2.14 to create an set of images from the Atlas tool, and it works fine as usual. However, instead of having each map iterate through the dataset and show one row of data at a time, I'd like it to show one row of data and then add each row of data successively in a cumulative way. I think I can use a rule to achieve this, but not sure how.
To help explain, see this gif I created from a series of maps on US gun crime. Instead of one day's worth of data appearing at a time, I'd like it to build up over time so that on the Jan 31 frame there is 31 day's worth of dots on screen and then it's just a mess of dots by Dec 31 - I know it will probably look bad but I'd like to use it in other projects as well.
Does anyone know how this could be done?