Exercise 4: Introduction to IDRISI

1N1663 Spatial Planning with GIS Period 3 Division of Geoinformatics 

Exercise 4: Introduction to IDRISI 

1. INTRODUCTION TO IDRISI 

Recommended readings: 

P:\WIN\Idrisi32\Documentation\Guide1.pdf 

• Introduction to GIS: p 5-16. 

• Idrisi system overview: p 35-37, p 41-42, p 44-55. 

2. IDRISI SYSTEM OVERVIEW 

The aim: 

1. Aquire knowledge about the program interface; 

2. Aquire knowledge about metadata (data that is used to describe other data) from the map 

layer data files; and 

3. Aquire knowledge about the program files. 

2.1. Start IDRISI: 

Start/ programs/L/Idrisi32 

After launching Idrisi, you are presented with the main window in which nine menus are 

found: File, Display, GIS Analysis, Modeling, Image Processing, Reformat, Data Entry, 

Window List, and Help. Collectively, they provide access to almost 200 analytical modules, as 

well as a host of specialized utilities. The Display, Data Entry, Window List and Help menus 

are fairly self-evident in their intent. 

Moving your mouse slowly over all the icons in the IDRISI main window (see graphic 

below), you will be presented with the names of each tool/function. Take some time to 

become accustomed to the names, as you will be asked to launch these tools/functions later in 

the exercise. 

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a. Management 

• Use the Windows Explorer to create a main working folder in your home 

directory on the H: drive (for instance: “H:\Idrisi\Working_folder” 

• Create a path in Idrisi to the main working folder by choosing File/Data Paths in 

Idrisi 

• Extract the files in the zipfile : G:\KURSER\Geoinfo\1N1663\IntroIDRISI.zip to 

your working folder. 

2.2 Displaying Map layers 

Since the earliest days of automated cartography and GIS, map layers have been digitally 

encoded according to two fundamentally different logics—raster and vector. Click on the 

DISPLAY icon on the tool bar. Note that separate options are included for raster and vector 

layers, as well as a map composition option and palette files. Select raster layers and double 

click in the white area to load your image (Display/Display launcher/ Raster 

layer/westluse.rst) – leave all other options as default. 

Double click 

here to load 

an image 

2.2.1 Now select the Cursor Inquiry Mode icon on the toolbar (the one with the question mark 

and arrow). When you move the cursor into the map display, notice that it changes to a crosshair. 

Click on different polygons in the map. 

2.2.2 Then click on the Feature Properties button in the Composer – see diagran below (or on 

the Feature Properties tool bar icon to the immediate right of the Cursor Inquiry Mode icon)-, 

and continue to click on polygons. Note the information presented in the Feature Properties 

box that opens below Composer. 

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Feature 

properties in 

the Composer 

2.2.3 Click on the Add Layer button in the Composer. This dialog is a modified version of 

Display Launcher with options to add either an additional raster or vector layer to the current 

composition. Any number of layers can be added in this way. In this instance, 

select the vector layer option and choose westroad.vct. (You can switch on and off layers by 

clicking to the left of the file name in the Composer.) 

2.2.4 It is possible to change the position of the layers by dragging and dropping a layer. The 

order of displaying layers in IDRISI is the opposite to ArcGIS. A layer at the bottom of the 

list in the Composer will appear on top in the map. Make sure that your vector layer, 

westroad.vct, is “below” your raster layer in the Composer. 

2.2.4 Select the westluse layer in Composer. Then click on the Layer Properties button. Layer 

Properties, as the name suggests, displays some important details about the selected 

(highlighted) layer, including the palette or symbol file in use. Have a look at the properties 

and then close the windows by using: Window list/ Close all windows (This will close ALL 

windows open in IDRISI). 

2.3 Examining and managing your IDRISI data files. 

Launch the IDRISI File Explorer (either by clicking on the icon or by selecting File/ Idrisi 

File Explorer). The IDRISI File Explorer is a general purpose utility for listing, examining 

and managing your IDRISI data files. The left-hand panel lists all of the various file types that 

are used in IDRISI, while the right-hand panel is used to select a specific file. When you open 

Idrisi File Explorer, it automatically lists the files in your working folder. However, the drop- 

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down list box to the upper-right can be used to select any of your resource folders or selected 

system folders. 

Highlight the westluse layer by clicking on its entry in the right-hand panel. Notice that the 

name is listed as "westluse.rst". This is the actual data file for this raster image, which has an 

".rst" file extension. Notice, however, that the panel on the left indicates that operations on 

these files also involve a second file with an ".rdc" extension. The ".rdc" file is its 

accompanying metadata file. The term metadata means "data about data", i.e., documentation 

(which explains the "rdc" extension—it stands for "raster documentation"). 

2.3.1 Now with westluse highlighted, click on the View Structure button. This shows the 

actual data values behind the upper left-most portion (8 columns and 16 rows) of the raster 

image. Each of these numbers represents a land use type, and is symbolized by the 

corresponding palette entry. For example, cells with a number 3 indicate forested land and are 

symbolized with the third color in the westluse palette. Use the arrow keys to move around 

the image. Then exit from the View Structure dialog. 

2.3.2 Making sure that the westluse raster layer is still highlighted in IDRISI File Explorer, 

click on the View Metadata button. This button accesses the Metadata module (also accessible 

from the File menu or the fourth icon on the tool bar) which shows us the contents of the 

"westluse.rdc" file. This file contains the fundamental information that allows the file to be 

displayed as a raster image and to be registered with other map data (i.e. georeferenced). 

The file type is specified as binary (A data file format in which numbers are stored in binary 

representation. In IDRISI, binary files require 1 byte/number for integer data, and 4 

bytes/number for real data. Binary files are more efficient than ASCII files for storing 

numeric data.). IDRISI also provides the ability to convert raster images to an ASCII format, 

although this format is only used to facilitate import and export. 

The data type is byte. This is a special sub-type of integer. Integer numbers have no fractional 

parts, increasing only by whole number steps. The byte data type includes only the positive 

integers between 0 and 255. In contrast, files designated as having an integer data type can 

contain any whole numbers from -32768 to + 32767. The reason that they both exist is that 

byte files only require one byte per cell whereas integer files require 2. Thus, if only a limited 

integer range is required (as in the case of westluse which has 13 classes), use of the byte data 

type can halve the amount of computer storage space required. Raster files can also be stored 

as real numbers, requiring 4 bytes of storage for each number. 

The columns and rows indicate the basic raster structure. Note that you cannot change this 

structure by simply changing these values. Entries in a documentation file simply describe 

what exists. Changing the structure of a file requires the use of special procedures (which are 

extensively provided within IDRISI). 

The seven fields related to the reference system indicate where the image exists in space. The 

Georeferencing chapter in the IDRISI Guide to GIS and Image Processing Volume 1 gives 

extensive details on these entries. However, for now, simply recognize that the reference 

system is typically the name of a special reference system parameter file (called a REF file in 

IDRISI) that is stored in the GEOREF sub-folder of the IDRISI program directory. Reference 

units can be meters, feet, kilometers, miles, degrees or radians (abbreviated m, ft, km, mi, deg, 

rad). The unit distance multiplier is used to accommodate units of other types (e.g., minutes). 

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Thus, if the units are one of the six recognized unit types, the unit distance will always be 1.0. 

With other types, the value will be something other than 1. For example, units can be 

expressed in yards if one sets the units to feet and the unit distance to 3. 

The positional error indicates how close the actual location of a feature is to its mapped 

position. This is often unknown and may be left blank or may read unknown. 

The resolution field indicates the size of each pixel (in X) in reference units. It may also be 

left blank or may read unknown. Both the positional error and resoltuion fields are 

informational only (i.e., are not used analytically). 

The minimum and maximum value fields express the lowest and highest values that occur in 

any cell, while the display minimum and display maximum express the limits that are used for 

scaling (see below). Commonly, the display minimum and display maximum values are the 

same as the minimum and maximum values. 

The value units field indicates the unit of measure used for the attributes while the value error 

field indicates either an RMS value for quantitative data or a proportional error value for 

qualitative data. 

The value error field can also contain the name of an error map. Both fields may be left blank 

or read unknown. They are used analytically by only a few modules. 

A data flag is any special value. Some IDRISI modules recognize the data flags background 

or missing data as indicating non-data. 

2.3.3 Now click on the Legend tab. This contains interpretations for each of the land use 

categories. Clearly it was this information that was used to construct the legend for this layer. 

You can now close Metadata. 

2.4 Symbol Workshop for Palettes 

Now open Symbol Workshop: Palettes to examine a palette named westluse.smp (Display/ 

Symbol Workshop). Symbol Workshop is used for creating and editing IDRISI symbol and 

palette files. These files record the graphic renditions for up to 256 symbols. From the Symbol 

Workshop’s File menu, you can open an existing palette file. In this case, open westluse.smp. 

(Hint: You will need to check the Palette option) 

Select Palette 

before opeing 

westluse.smp 

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The 256 symbols are displayed in a 16 x 16 grid. To edit a symbol, double click the particular 

symbol grid cell. The index number of the symbol (0-255) will appear as you move the cursor 

over each grid cell. Each number in the grid corresponds to the numbers (values) in the legend 

(Load westluse.rst using Display, and IDRISI File Explorer to compare the legend for 

westluse.rst). 

Experiment by changing some of the colours in the palette. When you are finished, save your 

new palette with a different name. Display westluse.rst with your newly created palette file 

(Hint: Use Layers properties from the Composer to apply your new palette). 

3. MAP COMPILATION 

Using what you have learnt above, make a map of Wesboro in which include land use and 

roads. The map should contain the following items: 

• Legend for land use; 

• Legend for roads (you should create your own legend palette for roads as there are 

three levels of roads – assign appropriate colours); 

• Scale bar; 

• North arrow; 

• Your names (using Text Insert from Map Properties) 

The Map Properties box can be used to for inserting scale bars, north arrows, text, etc. It is 

accessed from the Composer. 

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You should also provide a brief definition for the abbreviations listed below: (Hint: Use the 

Help menu) 

.rst 

.rdc 

.vct 

.vdc 

.rcl 

.avl 

.adc 

.mdb 

.map 

.smp 

.iml 

.imm 

.exp 

Once you have finished making the map and defining the abbreviations, you need to 

show Duncan the completed map on the computer screen and you should also submit a 

print-out of the map together with the answers to above abbreviations. A full report is 

not required for this exercise. 

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Exercise 4: Introduction to IDRISI

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