Unable to export spatial graph as PNG file in spatial graph viewer extension when spatial domain is very large

[rabotin]

• For a spatial domain with more than 10 000 spatial units only SVG export works

[jctophefabre]

The PNG export feature is a Qt built-in method, and cannot be modified. Maybe a warning dialog (abort/continue) can pop up for large domains (what is a large domain? maybe depends on computer performances?)