Using Location-Allocation to determine % demand that is supplied for shortest distanc

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04-24-2013 11:36 AM
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Hello --

I am new to using Network Analyst -- and currently exploring the Allocation-Location options of ArcGIS 10.1.  I am trying to find the right tool to distribute a fixed supply of vegetables (pts. of supply) to consumers (pts. of demand) in terms of least cost (as distance).  Using the Maximize Capacitated Coverage option, I can see the facilities that distribute to the demand points using the SHORTEST distance criteria.  HOWEVER, this RESULT does not show (1) the supply utilization --> how much of the total supply (capacity) has been distributed or (2) the demand fulfilled --> how much of the demand was met (in terms of % demand met at each point).

Can someone please let me know if I am using the right tool -- or if I need to use a combination of tools to solve this problem?

Thank you,
Jamie P.
Doctoral student in Ag, Food and Environment at Tufts University
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You are using the right tool (If I understand the problem correctly). And the information you are looking is available. It is on the facilities table. Each chosen facility has fields that tell you how many demand points and sum of demand assigned to them. You can sum up the total demand and the total supply and the total demand allocated and do the division to find the percentages.
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Thank you Mr. Jay Sandhu for the speedy reply.  I will try your suggestions later today once I am in the GIS lab.

I appreciate your feedback.

Have a good Thursday,
Jamie
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Hello again Mr. Sandhu:

Using your feedback, I investigated the Facilities table.  I understand the column "Capacity" refers to the total available supply for each facility and "Demand Count" refers to the number of demand points that receive some (or all) of their need from the facilities.  However, which column represents the "demand assigned to them"?  I see two other columns that are helpful --> "Demand Weight" which in my case, is equal to "Demand Count" since the weights are all 1.  The other column is "Total_Length" that I believe represents the cost (in my case, length in miles) for a product to go from the facility to the point of demand.

Also, in the ArcGIS help information for Maximum Capacitated Coverage, it states that "an allocated demand point has all or none of its demand weight assigned to a facility; that is, demand isn't apportioned with this problem type".  First, what is meant by Demand Weight?  Then, what does that statement above mean? Does it mean that a demand point will only get either 0% OR 100% of its demand needed?  For instance, a demand point can not get 50% of its demand needed? 

Finally, does this tool allocate from multiple facilities to a single demand point to satisfy demand?  If so, where in the table can you find (1) the facilities contributing to the demand point and (2) the amount each facility is contributing?

Thank you for any assistance with these questions.
Sincerely,
Jamie in Ag, Food and Environment at Tufts University
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Jamie,
First, a demand point can only be allocated to one facility. So if a demand point has 10 amount of demand and the facility only has a capacity of 8 then that point will not be allocated. That is, a fractional demand of 8 will not be split out and assigned to one facility and rest 2 to another facility. If you need to solve such problems then you could split the demand yourself. That is, enter the demand point more than once with less demand, e.g. enter it as 5 points with demand of 2 each. Similarly two facilities cannot be assigned to the same demand point.


Now for the Maximum Capacitated Coverage, after the solve, the facilities table has DemandCount and DemandWeight fields. The DemandCount tells you how many demand points were allocated to that facility, e.g., 4. The DemandWeight will tell you the amount of demand (summed from the 4 demand points) that were assigned to the facility. If the demand weight is 1, then it will also be 4 in this example. The amount of DemandWeight assigned to a facility cannot exceed it's capacity. The Total_Length tells you the sum of shortest path lengths from each demand point to the facility.


On the Lines table, you will see the individual assignment. That is, which demand point is allocated to which facility and the individual distance to it.

As to what is demand weight? It is amount of "things" at that demand location. For example, a house hold (demand point) may have 3 school going children that need to be assigned to a school. So 3 will be the demand weight.

Regards,
Jay Sandhu
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