ensureIndex vs. createIndex for a geo $near queries?

I currently have my 2dsphere indexes setup with ensureIndex but I guess this is deprecated? So I should be using createIndex?

 Meteor.startup(function() {
    Collection._ensureIndex({"location.geometry": "2dsphere"});


My other question is that I’m seeing people use createIndex without the underscore first-- is this the correct usage? Is there any reason to not include the underscore?

I checked stack overflow but there were differing answers

Hi, do you find any answer for your question?

I’m interested to know too but it’s weird that no one give an explanation here.

Not many use mongodb geo spatial feature in meteor?