CS 128/ES 228 - Lecture 9a1 Geocoding and Routing Ya can’t get thereah from hereah!

CS 128/ES 228 - Lecture 9a 1

Geocoding and Routing

Ya can’t get thereah from

hereah!


The Traveling Salesman Problem (TSP)

A Salesman must visit each of N cities and return to his home base, driving as few miles as possible

Insert Joke Here


Difficulty of TSP

Of interest to theoretical computer scientists

because

The Problem Is HARD

So hard that if you could compute an exact solution efficiently, you could also disrupt the world’s financial markets


Applications of TSP

Inspection routes

Traveling Salespersons

Delivery professionals


Knowing Where You Are

GEOCODING “is the process of converting an address into a point location.”

McDonnell and Kemp, International GIS Dictionary, 2nd Ed., 1998

“Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go,

there you are.”

Buckaroo Banzai (from The Adventures of Buckaroo Banzai Across the Eighth Dimension)


TIGER Maps – The Key to Routing

TIGER mapsare the primary data set used for geocoding.

… and geocoding is the basis for all routing.


TIGER Map of the Area

Dr. Levine’s House


TIGER Attribute Data


Some Useful Fields

FID Field ID Number

LENGTH Length of full extent

FNODE Intersection of “start” of street

TNODE Intersection of “end” of street

FENAME Street name (root)

FRADDR # of first house on RIGHT side

TOADDL # of last house on LEFT side

ZIPR Zip code of RIGHT side


How to Find an Address

1. Find the records for the appropriate street. (There may be more than one.)

2. Find the particular record whose address range includes your house number.

3. Decide “left” or “right” based on parity.

4. Interpolate.

23


But Apply Georgian’s First Law

Don’t process the data yourself; get someone else to do it

(of data processing)

http://www.mapquest.com


Limitations of Geocoding

Mapquest says Dr. Georgian lives here

Dr. Georgian says he lives here

Whom do you believe?


Why Is It Wrong?

FRADDR 3179

TOADDR 3297

FRADDL 0

TOADDL 0

Where is Dr. Levine’s House?

(#3299)


A Common TIGER Error

TIGER Files commonly miscode the F… and T… fields.

This results in various “mirroring” errors.

Newer versions of the data make this error less frequently.

Both Dr. Georgian and Dr. Levine are “victims” of this kind of error.


Other TIGER Errors

This road does not exist!

Data Lag

causes errors as new roads are (or are not) built


How Do We “Really” Do It?

By following instructions in tomorrow’s lab!


Going “Big” Time

One can easily geocode many addresses at once.

Place them all in a table and then ask the system to do so.

This gives you all of your “hot” locations.


Now, How Do You Visit Them All?


How many ways are there?

For 20 stops, there are

20x19x18x…x3x2x1 =

2,432,902,008,176,640,000

Possible routes! (that’s 2 quintillion)

Once again, we cannot be exact

Once again, we need a GIS


A Simple (non-)Solution Choose the route yourself

It turns out that humans, particularly experienced humans, are good at this

Then check only your 3 (or 40) best guesses!


Working with Simpler Routes

So it can be done

And we can’t do it


A Poor Man’s Solution

1. Select the lines that comprise your route.

2. Create a layer out of the selection.

3. Create a query that sums the lengths of the roads.


Conclusions

• Finding, Creating, and Measuring routes is a key task of many GIS’s.

• With ArcMap, we can do this for Points (geocoding), but not for extended routes.

• There are some “workarounds” we can use.

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CS 128/ES 228 - Lecture 9a1 Geocoding and Routing Ya can’t get thereah from hereah!

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