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(the name says it all) and

Washtenaw_nlcd_1992.shp (land use).

Making Things Look Right

Unfortunately, upon loading the

shapefiles, the sum total map that’s

displayed on the right in the Map

View window looks like a big rectan-

gle covered with random black and

green blobs and no lines. Where are

the roads, lakes and rivers I loaded?

One reason for the odd display and

missing elements is that the layers I

added first are buried under the

county-wide land-use layer, which sits

on top of everything else. I can begin

to solve this problem by dragging the

land-use layer down to the bottom of

the Legend and tinkering with the

other layers so they all are visible.

The other reason for the strange-

looking map is that QGIS defaults to

display one color for every characteris-

tic in the shapefile. For the road layer,

defaulting to one color is fine, because

it is simply a collection of lines.

However, layers with thousands of

polygons are more complicated. All of

the many land-use types default to the

same color, thus creating no differenti-

ation among them. I must give each

land-use type its own unique color

manually. To do so, I first right-click on

the land-use entry in the legend and

select Properties from the menu. On

the Symbology tab, I change the drop-

down menu next to Legend type from

the default value of Single Symbol to

Unique Value. Using the drop-down

menu in Classification Field, I can

select which field in the database to

classify. In my case, I classify a field

called GRIDCODE, which contains the

code that designates the land-use

code for each polygon in the layer.

How do I know which database

field I should classify, as well as the

meaning of each classification? To

find out, I sometimes need to leave

the Layer Properties menu and exam-

ine the attribute table, a display of

the database containing the attribute

data for the layer. For example, I can

examine the attribute table of the

land-use layer by right-clicking on the

title in the Legend (on the main GUI)

and selecting the command Open

attribute table. An example of an

attribute table is shown in Figure 2.

The land-use attribute layer contains

a field ID to designate each polygon,

as well as the field GRIDCODE to clas-

sify each one. Oftentimes the

attribute table also contains a field

with the label for each classification.

Although such a field is missing from

the land-use attribute table, a sepa-

rate file with classifications is found

in a text file included in the down-

loaded dataset.

After consulting the attribute table

and the file containing classifications,

I am ready to continue with the classi-

fication of the field GRIDCODE back

in the Layer Properties menu. Pressing

the Classify button populates the win-

dow below with the unique classifica-

tion codes found in the layer. I can

label each classification as I wish using

the "Label" field, and I can give each

classification its own color with the

Fill color option.

After finishing the classification,

I also want to do some more house-

keeping to make the Legend and

Figure 2. The attribute table displays the data contained in a particular layer, for example, a shapefile.

If you often have multiple putty, terminal, ssh or screen ses-

sions connected to various remote servers, one good way to

organize them is to have a small script that places the name

of the remote server in the title bar:

#!/usr/bin/perl -w

$name = $ARGV[0];

unless ($name) { $name = `/bin/hostname` }

print "\033]0;$name\007";

Save this, and make it executable. If, for example, you save

it as name, you simply can run name to place the name of the

current server in the title bar of your current session.

If you want to label the session with something besides

the hostname of the server, just specify the label on the

command line:

# name "Mail Server"

—FRED RICHARDS

TECH TIP

Server Name in Title Bar

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