GIS Virtual Workshop: Bufferinglegacy.jefferson.kctcs.edu/techcenter/pdf/gis/buffer.pdf · GIS...

1 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296

E-mail: [email protected]

http://techcenter.jefferson.kctcs.edu/workshops/

Vince DiNoto

Dean of College and Systemic Initiatives

Professor of Physics and Astronomy

Jefferson Community and Technical College

1000 Community College Dr.

Louisville, KY 40272

GIS Virtual Workshop: Buffering

This workshop will teach the different methods of buffering data. They will include:

Basic buffering of data

Merging buffering zones

Clipping the buffer

Concentric rings around the object

You will find multiple types of information available on the website which will include sample data, video and

web based content. http://techcenter.jefferson.kctcs.edu/workshops/buffer/Pages/default.aspx.

The starting point for this module is that you should have ArcMap open and have loaded five data sets:

KCTCS college locations (point), Kentucky Roads (line), Kentucky State Boundaries (polygon), Kentucky

County Boundaries (polygon), Kentucky Zip Code Boundaries (polygon). You can download these shapefiles

from the website, they will be in a compressed format (zip). You can choose geographic information of your

own region if you would like, but you need a point, line and at least two polygon shapefiles of the same coor-

dinate and pro-

jections. Turn

off all layers ex-

cept state bound-

ary. The color of

your layers may

look different.

http://techcenter.jefferson.kctcs.edu/workshops/buffer/Pages/default.aspx

2 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







Double click on the State

Boundary Layer Color Box to

display the window like the

one to the right. We want the

color of the fill for the map to

be hollow, so that other layers

can be displayed through this

layer. Double click on the

hollow icon, then click on the

properties button to display a

window to change other prop-

erties.

3 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







Once you selected the hollow fill it created a black outline

around the state. In this step you will change the outline to be

a standard state border. The window displayed to the left is

only a part of the window that will open. Click on the outline

button to open a window to change the property of the outline

for the state of Kentucky shapefile.

Select the Boundary, State

from the list of line types.

Note there are many other

types of lines that might be

used in other parts of this

module or other modules.

4 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







The white area of the map is really hollow, but

since all other layers are currently turned off it

appears white.

The next step is that we want to display the

county boundaries on this map. Click the check

box next to the county boundary layer to turn it

on.

Once the county boundary layer is turned on it

should look something like the map to the right.

The color of the fill may be different. We want

to make the fill for this map hollow and the

boundaries represented with the standard county

boundary representation. You will need to do

the same steps as was previously done for the

entire state. The one difference is selecting the

boundary as county boundary instead of state

boundary.

5 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







The resulting map should have an appearance

similar to the one on the right. At this scale it is

a little difficult to see the difference between the

state and county boundary information, but

when you enlarge a region you will be able to

observe the differences.

Next turn on the zip code layer by clicking the

check box. It should look like the map to the

left. The fill color maybe different. Again we

want to make the fill hollow and change the

boundary lines to being neighborhood. You will

follow the same steps as done for the state or

county layers to complete this operation.

6 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







The results of changing the fill and boundary

type for the zip code layer should produce a

map similar to the one at the right.

Next you will turn on the KCTCS layer. This is

a point shapefile and it maybe difficult to see

the dots for each campuses at this scale. The

campuses are represented by a dot and we want

to change the symbol to a school symbol with a

larger size.

Click on the dot symbol in the layer menu for

the KCTCS layer to open the following dialog

box.

7 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







Select the School 2 symbol

and keep the color with the

default green color and the

size as 18. You can change

these later by clicking on the

symbol to open this window

again.

The results of this operation can be seen in the

map to the right. You can now see the locations

of the KCTCS campuses and see that a more

appropriate symbol is being used. The refer-

enced point is the center of the symbol.

8 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







Next we want to turn on the road shapefile

(line). There are many different types of road

classifications. They are in general classified by

a code known as, Census Feature Class Codes

(CFCC) a description of these can be found at

http://www.census.gov/geo/www/tiger/

appendxe.asc. The road file that you have

loaded has only the major roads and does not

include city and county roads, but does include

state and interstate highways. For our work we

will not worry about classify-

ing the roads as different

types. Click on the road sym-

bol in the layer menu to select

the roads display properties.

Click on the Major Road sym-

bol, leave the color and the

width at the default levels.

You may wish to change the

width later so that the display

is easier to view.

9 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







We have now modified the data appropriately

from the initial load of information. If we are

viewing the entire state there are far to many

layers turned on for any meaningful information

to be obtained. Some of these layers are more

useful when we are at a zoom level of one or a

few counties. If the map was being plotted on a

large scale plotter than all layers could be left

on, but for a desktop size map we need to turn

off some of the layers as we view the entire

state.

Turn off the road and zip code layers, do not

remove the layers from the map.

Click on the toolbox symbol. Next click on

the Analysis Tools and the Proximity tray to

show the Buffer tool. In a later part of this

module we will also use the multiple ring

buffer. Select the buffer tool. Note in

ArcMap 9.1 the buffer tool was also in a

menu known as the Tool Menu. The view to

the right is only part of the full screen, you

should see your map to the right of the part

of the screen currently displayed.

10 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







The pull down

arrows next to

the boxes allow

you to use files

that are open on

your map. The

open folders icon

are used for files

that are not open

on your map.

The input feature

will be the

KCTCS Campus

layer. The out-

put feature will

be a file that is

created by the

process of buffering, you need to note the name of the file and the storage location, you can change both of

these items before the process is completed. The distance is a linear distance and we will select 25 miles for

this example. All other items will remain at the default levels. In the image below we are using the pull down

arrow and the list

shown is of all

layers currently

loaded on our

map. We will

select the

KCTCS layer.

11 1/24/2008

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Fax: 502-213-7296



Vince DiNoto







Note the output

feature that has

been placed in

the second win-

dow. We have

inputted the dis-

tance of 25 and

selected miles

from the pull

down arrow.

Click on ok to

execute the crea-

tion of buffers. A

progress window

will open and

this may take

several minutes

to complete depending on the speed of your computer and the amount of information to buffer. The KCTCS

file is constantly updated so your final results may look slightly different. Note many of the buffers extend out-

side of the state boundary.

12 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







To make the cir-

cles remain within

the state bounda-

ries we will use the

clip feature. You

may wish to refer

to the module on

Clipping for more

details. The clip

tool is located in

the Toolbox under

the Analysis Tools

in the Extract

Tray.

The clip window

requires a file and

a boundary poly-

gon to clip with.

Our file will be the recently created buffer file

and the boundary will be the state boundary file.

Since both of these files are loaded you can use

the pull down arrows to select. The third win-

dow is the location in which the new file, the

clipped buffer file will be stored and the name

that the system assigns to it. Make sure the

name is appropriate and that the storage location

is part of your tree structure. The remaining

items in this window will use the default values.

The results of clipping against the state bound-

ary can be seen in the image at the left. Your

county boundary file should be a higher layer in

the layer menu than the new clipped buffer file,

so that the county boundaries display on top of

the buffer.

13 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







In the next part we want to dissolve the bounda-

ries between the circles. To do this we are going

to create a new buffer around the KCTCS cam-

pus locations. Therefore, you need to go back

to the toolbox and open the buffer window

again. We have expanded the buffer window to

see all of the different options that can be used.

Near the bottom of the window you see Dis-

solve Type. The default is None. We will

change this value to All. We will also need to

input the layer for buffer to be defined about

which is the KCTCS campuses. Remember a

new shapefile will be created and stored with a

default name and note the location unless you

changed the information in the second window.

You will also need to input a distance for the

buffer with units. The window to the right

shows the values filled in.

14 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







The results of the dis-

solve is that circles that

touch have been dis-

solved. The country

boundary shapefile

needs to be placed above

the buffer layer. Note

the information extends

outside of the state

boundary because we

have not clipped this

layer. If you wish you

can do a clip, as was

done previously.

The final part of this

module will be to create concentric rings around the campuses of different distances. You will need to go back

to the Toolbox and select Multiple Ring Buffer this time.

Remember buffering can also be done with lines and polygons, in this module we have only looked at point

shapefiles. You have already loaded road and zip code information and you should try to buffer these layers to

see the results of buffers around these geometries.

15 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







The multiple ring buffer window looks similar

to the standard buffer window and the first two

boxes are the same. Select the layer to be buff-

ered using the pull down arrows. Again we will

buffer the KCTCS campuses. The output fea-

ture will be automatically filled in, make sure

that it make sense both in storage location and

name. Input the first distance and click on the

plus button. Repeat this for two additional dis-

tances. In this example we have used 10, 25 and

35. Next select the unit, for this example we

will use miles. We have also turned on the dis-

solve option to ALL to dissolve overlapping

rings. In the window to the right you can see all

of the selected and inputted values.

16 1/24/2008

Phone: 502-213-7280

Fax: 502-213-7296



Vince DiNoto







The image to left is

the results from the

completed operation.

You will note that the

rings are dissolved,

they extend beyond

the state boundary

since they have not

been clipped. To bet-

ter understand the

results it would be

good if each distance

was represented by a

different color. To do

this you will need to

open the property

window and use the symbology tab. Select quantities and then select the field which has the distance measure-

ments, select a ramp color. You should have three classes since we used three different distances. For a final

map you should also move the country and state boundaries to a higher level and clip about the state boundary.

GIS Virtual Workshop: Bufferinglegacy.jefferson.kctcs.edu/techcenter/pdf/gis/buffer.pdf · GIS...

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