Lab 2 Preliminary Analysis

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1
Geography 464
Professor Timothy Nyerges
TA: Guilan Weng
Winter 2012
Assignment 2
Preliminary Analysis
1.
Introduction
Before we can begin our GIS analysis we need to have the geodatabase developed in lab
assignment 1. There is more to building a database than merely compiling data. Our
research objective is to find a location for a new waste water facility; therefore, we will
creatively generate new information from the available data. The new information that
we generate will serve as empirical evidence to support a location recommendation. This
is one way that empirically verifiable new geographical knowledge is produced. We
encourage you to think about this process as you progress in this work.
We are using data to create new information and the new information will serve as
evidence in support of an argument that we have been asked to make. We have been
asked to argue for a recommended location for this new facility. A good argument
requires empirically verifiable knowledge and the new knowledge we produce will be
used for making an intelligent location decision. This said, we encourage you to think
about how data, information, evidence and knowledge can lead to greater wisdom –lead
to a wise location decision. Towards this end, we are building a geodatabase so that we
can systematically model the data and produce new information. We will create a value
structure by generating criteria data sets with key thematic layers and feature classes.
1.1 Learning Objectives
Substantive: understanding how and why new information comes to light when
performing a preliminary analysis.
Methodological: learning how a GIS analyst performs a preliminary analysis for site
selection and understanding the work flow.
Methodological: learning how to produce decision support artifacts to communicate
the character of a preliminary analysis to a diverse audience.
1.2 Overview
1) These learning objectives will be achieved by conducting a preliminary analysis
characterized by inclusionary and exclusionary screening based on the
geodatabase you created in assignment 1.
2) You will produce tables, workflow diagrams and maps to communicate the values
driving your analysis, the work process you used to conduct it and the spatial
characteristics of the results.
3) You will synthesize the experience through short answer essay.
Geography 464
Professor Timothy Nyerges
TA: Guilan Weng
2
Winter 2012
1.3 Research Question:
Which parcels in King County are appropriate for consideration and which parcels are
not?
1.4 Deliverables
1) Graphical artifacts include:
 a simple thematic map that shows excluded and included
parcels,
 a table that shows the value structure, and
 a workflow diagram.
2) Answers to the following four prompts (no more than two pages)
a) In a short essay, explain what new information comes
to light when performing a preliminary analysis.
b) Describe the process of a preliminary analysis to
accompany your workflow diagram.
c) Describe the values and measured criteria associated
with your geodatabase to accompany your table.
d) We produced four artifacts: 1) an essay, 2) a workflow
diagram, 3) a table and 4) a map. Decide which one
best conveys the spatial distribution and discuss why.
1.5 What you will need
Your personal geodatabase comprised of King County data.
Read the the readings related to the lecture this week.
The following processes will be accomplished here.

Exclusionary screening of unsuitable parcels based on size of area.

Buffered feature class based on inclusionary and exclusionary criteria will be
created for all the data sets.

Feature classes will be overlayed by type (school, street) to reduce processing.

Feature classes will all be clipped to the project area.

Feature classes will be combined into one inclusionary and exclusionary feature
class.

A suitability attribute will be added to the parcel feature class.
3
Geography 464
Professor Timothy Nyerges
TA: Guilan Weng
Winter 2012
2.0 Process
(NOTE: You will be working with a number of files that you will have to keep straight,
so it might be helpful to decide on a naming system for each output file that makes sense
to you.)
1. Reduce the size of the parcel feature class by excluding parcels that are too
small.
The parcel feature class is approximately 150mbs and contains more than 500,000
records. We will reduce the size of the parcel feature class by exclude parcels that
are less than ten.
Managing and manipulating large files over the geography network can be
problematic. For this reason we suggest moving the 150mbs parcel file to the
C:\temp directory on your computer. This will make the process faster. You can
discard the 150mbs parcel file after you have created the new layer.
When working with large files, one *key* strategy in ArcMap 10 is to uncheck
the layer in the table of contents (TOC) so that it does not draw. You do not need
to see the parcels for this next step. Since the parcel layer has more than 500,000
polygons it takes a long time to draw. Don’t draw.
Use the “select by attribute” tool to select parcels that are ten
acres and larger. (if unfamiliar with this tool use the help
menu to learn about it) Before you select the qualified
parcels, you need to calculate the area of parcels.
Open the attribute table of parcels. Add a field name
SHAPE_area, with float as type.
Right click the heading of the new field SHAPE_area, select
calculate geometry. Select Area in property and then click ok.
It might take a while since this is a big file. Once the
calculation is done, you can conduct select by attribute based
on thes shape area.
After you have selected the parcels that are more than 10 acres, create a new layer of the
selected parcels. (43,560 sq ft per acre).
Choose Data -> export data to create a new feature class.
Rename the new feature class “parceltenacre”.
Remove the parcel shapefile.
2. Create buffers for the school feature class
Geography 464
Professor Timothy Nyerges
TA: Guilan Weng
4
Winter 2012
Add the school dataset to ArcMap. Buffer the school feature classe, save the results in
your analysis folder, and give the buffered feature class a name that indicate it is
buffered (e.g. schsitebuf and save it in your geodatabase in your student folder). A
buffer distance of 500 feet is recommended. The buffer tool is in the analysis toolbox
inside the proximity tools.
 ArcMap  ArcToolbox  Proximity  Buffer
3. Extract primary street from street network
Use the “select by attribute” tool to extract primary street from the street network. In
order to achieve it, you have to read the metadata of King County street network and
decide the “key” variable and the appropriate values for your selection.
Once you have selected the primary streets, create a new layer of the selected streets by
“export selected data”.
Rename the new feature class as primarystreet and save it in your student folder.
4. Create buffers for the street feature class.
Buffer the primary street feature class and give the resulting feature class a filename that
indicates it is buffered.
 Set distance = 150 feet
 Name output feature class (to indicate it is a buffered feature class) and save it
back into your folder.
5. Clip buffered primary street feature class to parceltenacre.
The next operation will limit the area of the feature class by clipping the feature class to
the parceltenacre. To extract a clip of the school feature class that is within the
parceltenacre:




ArcToolbox  Analysis tool Extract  Clip
Select the Input Feature class, which will be the buffered street feature class.
Select the clip feature class as parceltenacre
Put the output feature class in the analysis folder and name it to indicate that it is
both buffered and clipped (e.g. streetbuffclip).
6. Buffer the sewer coverage
Unlike the school buffers, which are intended to exclude areas around the schools from
consideration, the buffer around the sewers are intended to be included areas for
consideration. Create a buffer around the sewers by using the buffer wizard to buffer the
clipped sewer feature class. The buffer distance should be 1500 feet. Put the output
feature class in the analysis folder.
7. Buffer the wetlands, landslides and park areas
Geography 464
Professor Timothy Nyerges
TA: Guilan Weng
5
Winter 2012
These areas are representative of sensitive areas or areas where there are geologic hazards
and the buffers around them are intended to exclude areas from consideration. Use the
buffer tool to create buffers around the three remaining layers. Use 500 ft for distance in
each case, name the outputs appropriately, and save them back into your analysis folder.
8. Overlay the feature classes to create the final feature classes for analysis
At this point you have six clipped, buffered feature classes: schools, streets, sewer,
wetlands, landslides and parks. Now you want to create two layers: one has all the areas
that you want to include in your sitting process (street and sewer buffers); and the other
one has all the area you want exclude (buffers for landslides, parks, wetlands, and
schools).
Use the Union tool to create two feature classes: “inclusive” and “exclusive”.
Union two feature classes at a time, until you have two feature classes (inclusive and
exclusive) for all the buffers, clipped to parceltenacre. If the process takes too long, you
might consider click individual layers to parceltenacre and then union them.
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