Alps Field Class: pre-departure exercise

How to use ArcView

Steve Carver

The following pages describe how you can use ArcView (or ArcMap if you have been doing GEOG2590) to display and analyse the data required to answer questions in the pre-fieldwork exercises.

What is ArcView?

For those of you who have not already used this software package, ArcView is a desktop GIS or Geographical Information System. GIS is an important technology for the management and analysis of geographical information. In the context of the Alps Fieldclass you will be using the ArcView GIS to display and analyse geographical datasets such as altitude, vegetation and geology. The pre-fieldwork exercise set by Oliver, Pippa and Stuart all require you to access and use certain datasets for the fieldwork location. The software allows you to:

display geographical datasets
overlay datasets as a stack of maps
retrieve information for any point
calculate new variables and map these
visualise the landscape in three dimensions

The file names used in the pre-fieldwork exercises are contained in the following table.

File name	Description
geology.shp	ArcView shape file of geology showing split between acid and basic (alkali) rocks
insol50.asc	ASCII raster file containing calculated maximum potential solar flux in a year
dtm50.asc	ASCII raster file containing 50m resolution altitude data (meters above sealevel)
aspect50.asc	ASCII raster file containing aspect data - direction slope is facing (degree from north)
slope50.asc	ASCII raster file containing slope/gradient data (degrees from horizontal)
contours.shp	ArcView shape file of 100m contours from 50m terrain model
vegpnt.shp	ArcView shape file of vegetation sample points
sldtm25.asc	ASCII raster file containing 25m resolution altitude data (meters above sealevel)
slcont25.shp	ArcView shape file of 10m contours from 25m terrain model

How to start ArcView

ArcView can be run from any PC on the ISS network. To start ArcView simply click on Start>Programs>Mapping>ArcView. the following "crib-sheet" tells you exactly how to operate the software in order the retrieve the information required by the pre-fieldwork exercises.

The "Welcome to ArcView GIS" dialog box will ask you whether you want to create a new project with a new view or a blank project. Just click on the "OK" button.
The "Add data" dialog box will ask you whether you want to add data to the view now. Click on "Yes" and in the "Add Theme" dialog box use the directory and file buttons/scroll bars to select the data file you want to display/interogate. All the data files for the pre-fieldwork exercises are kept in a zip file and will be available up until the fieldclass departure date via this link of the resources web pages.
When you first open an ArcView "View" (as a map display window is called), two windows appear: one labelled "Untitled" which is a menu of open views, tables, etc. (and is nothing for you to worry about just yet); and another labelled "View1" where all you data will be displayed. Maximise the size of this window by clicking on the maximise/restore button at the middle top right of the window banner.
To view the data you need to tick the small box in the key that appears in the frame down the lefthand side of the View1 window. The data will be displayed in a colour scheme chosen by ArcView. You can alter this colour scheme by double-clicking on the item you want to change in the key to start the "Legend editor".

How to display data in ArcView

Further data layers (Themes) can be added by clicking on the large plus shaped icon (secon from left on top row) or by cliking on View>Add Theme and choosing a data file as above from the "Add Theme" dialog box. Please note the following:

To import ASCII terrain data files (dtm50, sldtm25, slope50, aspect50 and insol50) first load the 3D Analyst extension by clicking on File>Extensions and ticking the 3D Analyst box and clicking on "OK". Then click on File>Import data source... and select ASCII Raster from the drop down selection menu in the "Import data source" diaolog box and click on "OK". Click on "Yes" and "OK" in response to the next couple of dialog boxes and display the data.
Once displayed, data layers or themes can be zoomed in and out using the +/- magnifying glass icons and drawing a zoom window with the mouse.

How to interogate data in ArcView

Data layers displayed on the screen can be interogated by selecting the "i" icon from the far left second row and clicking anywhere on the data. The value for the data set selected at the point clicked on will be displayed in an "Identify results" table window. One or more data layers (Themes) can be selected from the key by clicking on them. Multiple Themes are selected holding down the Shift key while clicking with the mouse.
It is possible to revisit the values retrieved from an data theme by clicking on the appropriate item in the left hand column of the table.
For the feature data themes, all attributes are shown in the right hand colum, for grid data themes, the "value" item in the right hand column refers to the value of the data layer at that point (e.g. altitude in meters or slope and aspect in degrees) while the "count" item refers to the number of occurences of this value in the grid data theme.

How to derive slope and aspect from a terrain model

For Stuart's pre-fieldwork exercise you are required to interogate points on the Odenwinkelkees glacier for grid co-ordinates, altitude, slope and aspect. To do this, you first need to calculate the slope ans aspect data from the terrain data layer (sldtm25). To do this...

Import the ASCII data layer named sldtm25 as above and display
With this theme highlighted in the key, click on Surface>Derive Slope and display the result, then click on Surface>Derive Aspect and display.
You can now interogate these along with the altitude data as required in defining your glacier transect.

Getting help

ArcView GIS is a quite complicated and extensive package. Following the above instructions will enable you to at least complete the required pre-fieldwork exercises. Futher help can be obtained from the Help system or Steve.