TOPIC: What's the difference between bottom up estimate and cost aggregation

What's the difference between bottom up estimate and cost aggregation

I’ll take a stab at this - cost aggregation is just adding up different costs. So cost aggregation is a step taken during bottoms up estimating. When you identify the costs during the bottoms up method you aggregate them to come up with one number for the cost/budget.

In fact the definition of bottoms up in the pmbok says pretty much this.

Bottom-Up Estimating. A method of estimating project duration or cost by aggregating the estimates of the lower-level components of the work breakdown structure (WBS).