Geography Reference
In-Depth Information
Exercise 7-5 (Project)
Using Buffer and Overlay Together with Geodatabases
Now let's use the principles you just learned regarding buffering and overlaying to solve a somewhat more
realistic problem. In this exercise, you use feature classes that come from a feature data set in a personal
geodatabase.
The Getrich Saga
You have been presented with some potentially valuable information! In a western state, in a county
named Getrich_county, a miner long ago buried gold now worth
at
least
4 million dollars but was never
able to come back to dig it up. He buried it within 1900 meters of the
edge
of one of the wagon trails that
run throughout the county, but at least 300 meters away from the
edge
of the trail. He put it into sandy
soil—more than 2500 meters away from any of the old oil wells. It will cost two cents ($0.02) per square
meter to search for the treasure—using metal detectors and Global Positioning System (GPS) receivers.
You may assume that if the gold is in the area you search, you will find it.
This information comes to you by way of a friend/client who knows you are taking an excellent GIS course,
have access to an Esri ArcGIS software system, and have some data available. Your friend certainly
doesn't have money to launch the search, but he has some friends who have money to invest in the
search if the cost is low enough and the maximum cost is well known in advance. There is not nearly
enough money to search the entire county (besides, that would cost more than the gold is worth). For a
modest cut in the profits, you agree to create a map showing the areas where the gold might be buried
and to compute the total cost of searching those areas. You will do this by making a
personal geodatabase
feature class (PGDBFC)
named Look_Here that contains only the polygons representing the areas to be
searched.
The data sets for the problem are all contained in a personal geodatabase named PGDB_gold.mdb,
located in a folder named
[___] IGIS-Arc\Gold_Data
You have four feature classes to work with:
Getrich_County—A very simple POLYGON feature class of the county. The treasure is within
the outline of the county.
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Oilw—A POINT feature class of all the sites of the abandoned oil derricks and wells.
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Wagt—A LINE feature class of the centerlines of the wagon trails. (Each trail is assumed to
be 10 meters wide. Recall that the treasure is buried a certain distance from the
edges
of the trails.)
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Soils—A POLYGON feature class of the soils in the area. There are four types of soil: clay,
dirt, sand, and rock. You also have a separate table that indicates the soil types. In this
table is a column with the heading of Characteristic. The feature class contains a key that
will let you join this table with the feature class.
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