GIS 8746

Assignment #2
Where to Plant Eucalyptus: A climate investigation of Africa

Typography for this assignement:

  1. Questions in this assignment are numbered and bold
The goal of this assignment is to find areas of Africa where the criteria in Table 1 are met

Table 1: Prime conditions for growing Eucalyptus

Condition Value
Mean annual rainfall  70-250 cm
Rainfall Regime Summer or Uniform
Max. monthly mean temp. 31 deg. C. or lower
Min. monthly mean temp. -1 deg. C or higher
Mean annual temp. 14-22 deg. C.


Table 2: Data sets for this Assignment.

Image files Description
AFTOT88.IMG Total NDVI for 1988
ANNTMP.IMG Mean Annual Temperature
MAXHOT.IMG Max. Monthly Mean Temperature
MINCOLD.IMG Min. Monthly Mean Temperature
ANNPREC.IMG Annual precipitation
JANPREC.IMG to DECPREC.IMG Twelve Monthly total precipitation images
Vector files  
COUNTRY.SHP Country polygons for Africa
Other files  
COUNTRY.TXT Contains names of countries. The numbers will be related to the pixel values in the COUNTRY image that you generate in this assignment.

  1. File size is often an issue in storing and analyzing data. Why do you suppose the temperature data (e.g. MAXHOT) is stored in units of 0.1ºC?
Since "Rainfall Regime" is one of the criteria that must be met, we have to define and create an image for this factor. Table 3 shows the three regimes that we will classify.

Table 3: Rainfall Regimes defined

Regime Condition
Summer summer rainfall > 30% greater than winter rainfall
Winter winter rainfall > 30% greater than summer rainfall
Uniform neither winter or summer
Since Africa spans hemispheres, we have to be clear about our definition of Summer and Winter.

Table 4: Seasons defined

Month Range Season/Hemisphere
May - October Summer/North - Winter/South
November - April Winter/North - Summer/South
BEWARE: These definitions of Summer and Winter should be carefully considered when answering questions!
  1. Summer precipitation is highest in what parts of Africa? (perform the following steps to define the area).
  1. What is the maximum value in MAYOCTPR?
An ArcView shape file entitled COUNTRY.SHP has been provided. This file contains polygons representing the various countries of Africa. Since we will be using this file in analysis, it must be converted to raster format. However, since IDRISI does not read shape files natively, the shape file must first be imported into IDRISI (SHAPEIDR converts ArcView Shapefiles to IDRISI for Windows vector files and IDRISI for Windows vector files to ArcView Shapefiles).
  1. Provide a list of the top three countries in terms of highest average summer precipitation?
Now we will define the Rainfall Regime. The most efficient way of doing this is taking a ratio of summer and winter images (i.e. MAYOCTPR / NOVAPRPR). However, there is a problem. We must all 1 to both of these images before we perform a ratio (especially NOVAPRPR).
  1. Why do we have to add one to MAYOCTPR and NOVAPRPR (but especially NOVAPRPR)?
  1. Referring to Table 3 that defined the Rainfall Regime, complete the following table with values in RATIO image. Use the following syntax (e.g. 1.8 < z < 2.4 or z > 2.4 or z < 1.8) where z represents the values in the RATIO image:
Table 5: Range of Values in RATIO image
Note that the Northern and Southern hemispheres have different ranges for summer and winter regimes. This is a problem! How can we reclass RATIO into a REGIMES image if we can't use the same ranges in the reclass?! (This is a rhetorical question, do not write down an answer, the answer will be developed as we progress in this assignment).

There are many different ways of solving this problem. Our approach will be to make the ranges for each regime unique by creating an image that has +1 in the northern hemisphere and -1 in the southern hemisphere (called CHANGER). This image will be multiplied by RATIO to give unique Regime ranges. Then we are a "reclass" away from our Regime image.

  1. After multiplying CHANGER and RATIO, what happened to the values in the northern hemisphere? What about values in the southern hemisphere? Would this method be appropriate if RATIO had positive and negative values in both hemispheres? Explain.
  2. What are the minimum and maximum values of NSRATIO?
Table 6: Rainfall Regime values for REGIMES image.
Rainfall Regime Value in REGIMES image
Winter 1
Uniform 2
Summer 3
The REGIMES image represents the final rainfall regime map.
  1. What can you say about the distribution of summer, winter, and uniform rainfall regimes in Africa?
  2. What do you notice along the equator? What causes this? Can you think of a way to produce REGIMES without having this occur?
  1. If there are only 1's and 0's in the resulting image, does that mean that the reclass was done correctly? How might an error be made that wouldn't be caught by checking that there are only 1's and 0's
  1. Which OVERLAY operation should be used?
  2. Which country has the largest area of land suitable for Eucalyptus? (HINT: Use EXTRACT).
  1. Which statistic to you use for EXTRACT? Why?
  2. Is there a difference in NDVI statistics for the rainfall regimes? Explain.

Back to Contents