Reduce memory footprint

[plepe]

Basemap in low zoom leves (5, 6, 7, ...) results in huge memory foot print, due to high amount of objects to be rendered. This issue collects ideas how to reduce memory usage.

• copy geometry to pseudo elements only when geo has been changed Property 'geo': do not initialize; rather access either prop or object as needed #67
• reduce memory consumption by using cursors Reduce memory consumption by using cursors #71