key to properly understand

[JEic]

Building the right definition of a slum is key to properly understand and tackle the problem of these unsafe informal settlements (https://www.habitatforhumanity.org.uk/what-we-do/slum-rehabilitation/what-is-a-slum/)

(1) I thought that gerunds should be used here: 'Building the right definition of a slum is key to properly understanding and tackling the problem...."

if I take out the word 'properly', it goes".....is key to understanding and tackling...."

Are both correct? I don't understand.

 

[emsr2d2]

The gerunds would also be correct. However, in the original, you can take "to" to mean "in order to". In that case, it's correctly followed by the bare infinitive.