Lab 3: Structuring data
In this lab you will put together a project, join external data to the existing and choose
which data should be presented and how.
The data that we’re going to use is located on the University server. We must access
this server before start working, and this is something we must do every time we work
with this kind of data. Right click the My Computer/Min Datamaskin icon on top of
your desktop. Choose Map Network Drive, complete the dialogue as shown below and
click Finish.
Part 1.
1. Open ArcMap. Choose to start with a new map.
There are two ways to add data to your project.
- If you know what you’re looking for, but don’t know what it’s called, open
ArcCatalog, search through the files using the preview function and drag the
files you like across to the ArcMap interface.
- If you know exactly which file you want, load them directly into ArcMap
using the Add Data button
.
2. Add the files n5000fyf and kyst from the Z:\gis\modul3 folder. Make sure that
n5000fyf, which is the Norwegian regional administrative units (fylker), is
placed below kyst (coast) in the table of contents hierarchy, so that both can be
seen.
3. In the table of contents, open the layer properties window of the n5000fyf
layer, choose general and change the name to Fylker.
4. In the table of contents, open the layer properties window of the kyst layer and
double click the box indicating the layer’s colour. You can change thecolour if
you feel like it. It would be a good idea to change the outline of this layer.
Choose outline and No colour.
We will make a survey of unemployment in each county for the year 2003.
There’s no data saying anything about this in the files we have uploaded, but we
can get the statistics somewhere else and use it in our own project. The table
ledighet.xls in the modul3 folder contains this info. ArcMap can’t read excel files,
but we can convert it to a format it can understand, e.g. dBASE (.dbf). This can be
done in MS excel.
5. Start excel and open ledighet.xls from Z:\gis\modul3
In .dbf files it is important to format each cell, row and column properly, otherwise it
won’t be intelligible to other programs. To format cells, make a selection of them,
right click inside the selected area, choose format cells and choose the appropriate
format.
The first row must only be used to label the field contained in the columns. The name
of the variable can contain 10 letters or digits only.
The columns must be wide enough to show all information, otherwise it will not make
it through to the dbf format. Select the columns, choose format, columns and auto
selection/beste tilpasning.
File names should not contain open spaces or other special symbols.
6. Format the table in ledighet.xls according to the above listed requirements.
Save it as a dBASE file (dbf4) on your M: domain. Some warning
notifications will appear, but as long as you have done your formatting
properly, you don’t have to worry about them.
In order for two tables in a database to be joined, they must have at least one variable
(column) in common where the units/elements (rows) are described in the same terms
in order to be matched to each other. In this case each of the geographically
referenced polygons representing the counties in the n5000fyf/Fylker layer ought to be
matched to its corresponding unemployment rate figure in the statistics contained in
the dbf file.
7. Open the attributes table of the Fylker layer.
8. Open ArcCatalog and access the table in ledighet.dbf, which should now have
been stored on your M: domain. Figure out which variable is common to the
two. If no variable can be used, change the table in excel so that it can and
save the changes.
To join an attributes table to an external table, select the layer in the table of contents,
right click and choose join. Complete the dialogue by browsing for the tables and
decide which variables to use as common reference.
9. Join the layer Fylker to the table ledighet.
10. Open the attributes table of Fylker to make sure the ledighet data has been
added.
To make the new data useful in our project we need to change the symbology of the
representation. By right clicking the layer in the table of contents and choosing
properties we can make certain changes to the appearance of the map. Symbology
determines what data is expressed in the map and in which way.
11. Choose Symbology and then Quantities. We want to express our quantitative
data in graduated colours. As Field Value, choose the variable that expresses
unemployment and click Apply.
The map now expresses which counties have the most unemployed people. To
express the unemployment rate we must use another variable, the number of people
between 16 and 74, which is the cohort that the Norwegian statistics SSB use for this
kind of purpose.
12. Return to Symbology. Choose the 16-74 variable to Normalise by. The
unemployment figures will now be divided by the population figure in each
county to produce the rate. Choose Apply.
13. Save the project on your M: domain and make a layout with a legend and a
title.
Part 2
1. Publish the results from part 1 on your web page
2. Map the differences of mean per capita emissions of CO2 from cars in
Norwegian municipalities/kommuner in the year 2000. Publish the map on
your web site with a legend that clearly explains what the map expresses.
Hints:
- The table co2.xls on Z:\gis\modul3 contains statistics on co2 emissions from
cars in Norway as well as population figures on the municipality level.
- The n500kof file contains the municipality borders.
- Lab 2 contains a walk-through of the layout functions in ArcMap.
Good luck!