Ok, I made some charts to demonstrate. The total discounted volume for bids and asks in USD is shown beneath each.

Here's the raw data I was working with
http://i.imgur.com/yPjLtle.png
Bids: 12170767.4644583
Asks: 27476862169015.9

And here's the depth chart up to twice the top bid
http://i.imgur.com/BRxe2b6.png

Here is the exponential discount factor I described before, it prioritizes prices close to the spread.

The formula for the discount on bids is e^(-a(highestBid-bid)), and e^(-a(lowestAsk-ask)) for asks.

Here's the discounted volume:
http://i.imgur.com/CSZjOCi.png
Bids: 105023.402931941
Asks: 23900.6565377794

That was a little too restrictive, relax the scaling parameter a bit to a=0.1:
http://i.imgur.com/K0SOpL1.png
Bids: 1522439.36415067
Asks: 1236490.55085024

It can be relaxed further to include points further down the line:
http://i.imgur.com/b8VT37W.png
Bids: 3262099.42799612
Asks: 2777887.40515259

Alternatively to give full weight to the majority of the orders, use 1-e^(-a*bid) for bids, and max(0, 1-e^(a*(ask-lowestAsk)-highestBid))) to create a symmetrical bandpass filter about the spread.

Here's what it looks like with a = 1:
http://i.imgur.com/1aToRt2.png
Bids: 11970104.7601015
Asks: 9177170.77805910

Restrict the further out values a little with a = 0.15:
http://i.imgur.com/PowevBb.png
Bids: 11091817.7195716
Asks: 8799423.98610072

A simple linear discount function, use 1-(highestBid-bid)/highestBid for bids and max(0, 1-(ask-lowestAsk)/lowestAsk) for asks
http://i.imgur.com/9b6neS5.png
Bids: 6158532.21541063
Asks: 5225588.99409854

Depending on what kind of analysis you want to make I'd say either the bandpass function with a=0.15, exponential function with a=0.1, or linear function would all work fine.