In that sentence, "at least as important as" compares:

• changes (in the geometric properties...)

with

• (simple) geometries.

The meaning is that the geometries:

• have the same importance as the changes;

or:

• have more importance than the changes;

but not:

• have less importance than the changes.

From the Cambridge Dictionary

at least = as much as, or more than, a number or amount:

• It will cost at least $100.
• It will be £200 at the very least.
• You'll have to wait at least an hour.

and:

Also from Cambridge Dictionary

As … as = We use as + adjective/adverb + as to make comparisons when the things we are comparing are equal in some way:

• The world’s biggest bull is as big as a small elephant.
• The weather this summer is as bad as last year. It hasn’t stopped raining for weeks.
• You have to unwrap it as carefully as you can. It’s quite fragile.