Forgive me but your documentation for how to use the MapPress widget is not entirely clear to me (more my fault than yours).
I have a map on a page with ID=317. The MapPress shortcode on that page is [mappress mapid="4"]. I would like that same map to appear in a footer widget but I am having trouble. Fyi, the page in question is http://belfield.nswact.uca.org.au/
So, since I only have one map on one page, I originally thought I could select “Show/All posts” in the widget settings, but that doesn’t seem to work, probably because the map is on a page. So, I set the “Custom query” to “page_ID=317”. Is this correct or should I do it another way?
Sorry for my slow reply. The widget is really meant for mashups more than for showing a single map, but the way you’ve done it should work (‘page_id=’ for a page or ‘p=’ for a post).
I have some other items to implement first but it’s been on my to-do list for a long time to add a widget for a single map ID. Let me know if this is something you need or if the workaround above is sufficient.