I make map with a overview in QGIS. I try to adjust my overview scale in relation with the first map scale. I explain : I want adjust overview scale with a factor 5 or 50, not fixed scale. When my scale is 1:1000 in first map, I want scale in overview is 1:5000, if first map 1:1200, overview 1:6000……
I look in expression but I don't find the good way.
Use the following expression in the expression string builder of the overview map:
map_get(item_variables('mainmap'), 'map_scale') * 7
... where in this example: 'mainmap' refers to my main map. You'll need to adapt it to the name of your own map you're refering to. (Usually map 0 or map 1).
7 is the factor I adjusted the scale with.
I had the same problem although my question was a little different. I wanted to scale the transportation symbols on Esri basemap from the map canvas at 1:100,000 to look right in my composer window overview map at 1:500,000.
In my map canvas I right-click the 1:100,000 scale layer and select "set layer scale visibility" to 1:500,000. In layer properties under the "rendering" tab I check the "Scale dependent visibility" box.
Now I go to my Map Layout Composer's "item properties" and set the scale for the overview to 1:500,000. All the symbols on the Esri transportation layer are just the right size to read in the overview, not too many or too few symbols for the scale.
