|
|
GIS Exercise 20 may 2003 |
Thomas
Gumbricht T.Gumbricht@cgiar.org |
Introduction to GIS and Digital Cartography using ArcExplorer
|
Requirements This exercise requires a PC with Windows 95/98/2000, Windows NT, or
later and the freeware ArcExplorer 2.0. To download and install ArcExplorer
see appendix 1. The necessary data are available on the RELMA_GIS1.0 CD.
Sources of internet available data are given in appendix 2, and in the
document Spatial
Data and Applications for Environmental Studies in Africa. |
|
Objectives This exercise will give an introduction to
GIS and digital cartography using the ArcExplorer freeware. To illustrate the
exercise different freely available data over Africa will be introduced. The objective
of the exercise is that the students should gain basic insight into GIS and
digital cartography including data types, scale, symbolizing, labelling and
layout. After completing the exercise students should be able to create
small-scale thematic maps. |
|
Task To pass the exercise a thematic map over Africa with major rivers and catchments, and population centers showing cities symbolised based on inhabitants should be handed in. |
Start the GIS freeware ArcExplorer and add data
In this exercise we will use ArcExplorer 
-
a GIS freeware offered by ESRI (ArcExplorer is the free viewer of ArcView)– see
appendix 1 for instructions on how to retrieve ArcExplorer from the internet
and set it up.
|
If the ArcExplorer icon is not on your desktop you can find it via “Start - Programs - Esri – ArcExplorer 2.0 – ArcExplorer”. The source program is under “C:\Program Files \Esri\ArcExplorer2.0”. Start ArcExplorer. |
Start ArcExplorer |
The main parts of the ArcExplorer interface are shown in the figure
below. You will be presented with an empty project called Untitled. The Legend window contains
two tabs (pages), one for Local themes (themes that are
stored on your local computer or local area network) and one for WWW themes (themes
stored on Web sites). In this exercise we will only use local data, to use WWW
data your computer must be connected to the internet. An introduction on using
internet data is given in the exercise Data Mining on Internet.
To get help on any topic just press F1, or search via help in the menu
bar. You can also find the users manual (Using ArcExplorer.pdf or Arcexplorer.pdf) in the same folder as
the program file. This manual can be read by using Adobe Acrobat reader (see
appendix 1 for download of Adobe Acrobat).
In the interface you will notice that some menu and
tool items are gray (fuzzy) that means that they are not available at the
moment. Many items require that you have some themes in the view, (a theme
is a maplayer in GIS jargong) and some that you have at least one theme
active (this will soon be clear to you).
|
Map View Legend Tool bars Menu bar |
Save, 
the ArcExplorer project, preferably in your
home directory. Change the name into something logical. Remember to save the
project frequently in case you should cause the program to crash or loose power
supply.
|
We will start by adding some maps from the RELMA_GIS1.0
CD. Press the Add Theme button, |
|
,
and go to the directory 
|
The Legend window should now contain 3 themes, as
shown to the right. The river theme is composed of lines, and the basin and
boarder themes are polygons. Click in the Check
box to the left of the AFRICA_BOARDERS
theme. You should now see the map of African countries in the Map View. Also
click the Check boxes
of the river and the basin theme – note the difference between themes with
lines and polygons. Use the Zoom In tool, |
Check box |
,
to zoom in on Africa and the 
Use the Zoom to Full Extent button,
to return to the full view. If you just click
in the view with the Zoom In tool active the
position you clicked will be the center of the new display area after the zoom.
Also try the Pan
tools, 
and 
.
Turn off the river and basin themes; we will only use them later in the
exercise.
Select and Find Data
|
Note that several
of the Tools are still fuzzy (i.e. inactive). Activate the AFRICA_BOARDERS theme by clicking on the label (not the Check box) and see how the active theme appears
‘lifted’. Now also several of the tools will be activated and have a full
color saturation. We will now
locate Uganda (or another country) in our view by using the Find tool, |
|
.
Click the find tool.
|
In the dialogue box Enter Uganda under 1.
select search type, set 2.
Select a search type to Any part
of Field, and 3.
Choose which theme to search to Africa_boarders.
The click the
and select 4. Pick
a feature to be Africa_boarders
CNTRY_NAME. Then 5. Select
the operation to perform, sequentially click the buttons
Uganda should appear in yellow in the Map View. Use
the Clear Selection
tool, |
|
,
,
and
.
Querying data
To see the database table for an individual country
use the Information tool,
.
Make sure that the theme Africa_boarders is
active (i.e. elevated), point at any country and click the left mouse button.
All the fields of the database for the selected country (a record
in database jargon) are displayed.
Next we will
try the Query Builder, 
to see which African nations are larger than
Sweden. The area of each country is given in square kilomters in the theme Africa_boarders.
|
Make sure Africa_boarders
is the active theme and click the Query Builder, In the query builder you can also calculate summary
statistics for numerical fields. Try it out for the area of countries. How
many countries are there in Africa, and what is the average size of the
countries in Africa? (The answer is 48 countries and 609474 km2) |
|
Next try to build a query to see which African
countries are larger than Sweden but at the same time have less population (the
population of Sweden is 9 million). The Query should look like this: SQKM_CNTRY > 500000 and POP_CNTRY < 9000000.
How many countries fulfilled this Query?
To clear the classification press the Clear Selection tool,
.
Symbolizing data
Use the Zoom to Full Extent button, to get the view of the whole of Africa. As
you can see all countries have the same color. We shall now symbolize the map
and the countries by putting different colors to them.
|
To set a background color and other map display
properties press View in the menu bar and then Map Display
Properties. You can add scrollbars and make the map appear 3D
and change the color of the Background
(the sea in our case) and Highlight (when
you query the data the result is highlighted in this color – yellow is
default). Click OK when finished. |
|
|
Make the theme AFRICA_BOARDERS active. Open the Theme Properties dialogue box, either via
the Theme properties button, |
|
,
or double click a theme’s name in the legend. Set 
|
To change the individual color (or other symbol) for
a particular record first open the Theme Properties box, simply click
an attribute and than select Color,
Style and Size. You can set individual colors, style and size
of each attribute by clicking on them. Try changing the color
of Uganda as shown below. To get to Uganda in the Discrete Values and Symbols menu you have to use the
scroll tools, |
|
|
If you have done everything correct, your map should now look like below.
Labeling maps
To label a polygon map in ArcExplorer you have to add
a duplicate copy of the theme. Use the Add theme button, 
,
and add a second copy of the AFRICA_BOARDERS
theme. Put the new theme highest up in the Legend (grab it by holding down the left mouse button and slide it
to the top of the legend).
Open the Theme
Properties dialogue for this second AFRICA_BOARDERS theme – either by double clicking, through the
right mouse button or under Theme in the menu bar.
|
In the Theme
Properties dialogue set Classification Options to be Standard
Labels. New labels and edit boxes will appear. Select NAME
as Text
field and deselect Draw features. You can also change the Font.
Press Apply and then OK. Your map should now have name labels for
countries in Africa |
4. Click Apply 3. Deselect Draw Feature 2. Set Textfield to CNTRY_NAME 1. Set classification option to be Standard Labels |
As you will see when you display the whole African
continent the name labels are too large; it is difficult to read the names as
well as distinguish which name belongs to which country. To improve the layout
of the map you can decide a scale above or below which the name labels will not
be displayed. First zoom the map of Africa so that you can conveniently read
the labels and associate them with a particular country. Activate the theme and
press the right mouse button, in the pop-up menu (see next page) select the
option Set Maximum Scale Factor. Zoom to
Full Extent, – and voila no name labels - if you
zoom in they will reappear.
|
|
To enlarge your View you can use the Toggle Legend button,
.
Try it.
Zoom to Full Extent. If
you followed the instructions no labeling should be seen. You should now add a
tool that allows you to use the mouse for displaying selected properties of a
theme. Make sure the visible AFRICA_BOARDERS
theme is active (the copy of this theme symbolizing colors). Click the Map tips tool,
,
to display the Map Tips
dialog. Select CNTRY_NAME in
the list and click OK. When you move the cursor in the view the name of the country
where you slide the cursor will be shown in a little box. Hands on your heart -
how many African countries do you really know?
Display overview map and add image
theme
|
|
|
|
|
ArcExplorer can display
georeferenced images as backdrops. Use the Add
Theme button, |
|
Make the image
theme the active theme (it should appear raised) and use the Zoom to
Active Theme
tool, 
.
Change the active theme to be the AFRICA-BOARDERS theme that you used for
setting the MapTips and move the cursor over the Map View – the name of the
countries will be displayed despite that you do not see them.
Composing a thematic map
We shall now
have a look at the drainage system of Africa. Click the Check box for the AFRICA_BASINS theme.
|
|
In the same way
click the Check box for the AFRICA_RIVERS Theme. Change
rivers to a blue color and line width to be 2 in the Theme Properties dialogue.
Set the scale and scale units
|
A scale bar is obligatory for a map. Thus you must
add one. This you do under View
in the menu bar as shown to the right. To change the scale bar to display
kilometers and be in centimeter units change the Scale Bar
Properties (also found under View
in the menu). Map units are decimal degree so you must not change them, set Scale Units to
kilometers and Screen Units to centimeters You also need to set measure
units to be able to interactively calculate distances in the map. This is
done under Tools
in the menu. Set the Measure units, |
|
You should now have a thematic map of Africa showing
rivers and major watersheds against a satellite image backdrop.
Your turn
To complete the
exercise you should put the national boundaries on top of the map (in black)
and add a theme showing major African cities (found in the file AFRICA_CITIES
in the directory …data/spatial/africa/infrastructure). The city theme is composed of point data.
Try to symbolize the cities according to number of inhabitants, as done in the
example on next page.
When you are
satisfied with your cartographic product it is time to transfer to another
media. Either print it,
|
|
AFRICA – major drainage system and population centers
Appendix 1: How to get ArcExplorer
from the internet
Use a web-browser (Netscape, Internet explorer) and navigate to ESRI´s
homepage (http://www.esri.com) and to the page
with free resources (in the blue field to the left, you have to scroll down get
to Free Resources), select ArcExplorer (you should then be
transferred to the site http://www.esri.com/software/arcexplorer/index.html).
Read about ArcExplorer and then press Download
(version
2.0 is the latest at the time of writing this instruction). You should then be
transferred to the page http://www.esri.com/software/arcexplorer/aedownload.html.
Download the file ae2seup.exe, also download the User Guide, arcexplorer.pdf.
Close all windows applications that are
running on your PC and install ArcExplorer by executing the program ae2setup.exe
(the program that you downloaded). To be able to install ArcExplorer you must
have administrative rights on the computer you are using – if you do not have
that you must ask your system administrator to help you. To install and run
ArcExplorer the user should have full access (read and write) to the archive
C:\Esri\ (not only for installation – also for running). When you install the
ArcExplorer the default path for installation is “Program files\ESRI\ArcExplorer”. It is recommended that you accept
that.
If you get stuck or do not understand a command, please refer to the User Guide that you downloaded (arcexplorer.pdf). This document is in pdf format, which you can read using Adobe acrobate reader. If you do not have acrobat reader on your computer you can download it from http://www.adobe.com/. Installation is done in a similar manner as the ArcExplorer installation described above.
Appendix 2: Free data from the
internet used in this exercise
Most of the data used in this exercise is freely available from the
internet. Most of it you can find via
ESRIs (the supplier of ArcExplorer and ArcView) home page www.esri.com Their
own main data can be found at ArcData online - http://www.esri.com/data/online/index.html.
Other data suppliers can be found under the page http://www.esri.com/data/index.html,
especially the data hound is useful for finding thematic data over specified
regions -http://nt1.esri.com/scripts/production/esri/marketing/datahound/main.cfm.
For more comprehensive information on data available over the internet
see the document Spatial Data and Applications for Environmental Studies in
Africa. The exercise GIS
Data Mining on Internet introduces using ArcExplorer for direct linking to
map resources on the internet. It also includes examples of how to find and
download other datasets, including Digital Chart of the World (DCW), which is a
comprehensive dataset with global coverage. DCW data covering the RELMA countries
(Uganda, Ethiopia, Eritrea, Tanzania, Kenya and Zambia) is available on the
RELMA_GIS1.0 CD (under …data/spatial/DCW). To import the DCW to
ArcExplorer you must use special software (Import71), which is also supplied on
the RELMA_GIS1.0 CD. It is however not trivial to import this data, but you can
find the instructions in the exercise Data Mining on Internet.