GIS 8746
Assignment #2
Where to Plant Eucalyptus: A climate investigation
of Africa
Typography for this assignement:
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Questions in this assignment are numbered and bold
-
Data processing steps are bulleted. However, please note
that not all processing steps are provided.
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. |
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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!
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Create images called MAYOCTPR and NOVAPRPR by adding all
the precipitation images from May to October and November to April respectively
(I love macros). After you have verified that all the images have been
added together correctly, you might want to delete the monthly precipitation
images since they will no longer be needed.
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Summer precipitation is highest in what parts of Africa?
(perform the following steps to define the area).
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Digitize a polygon with no more than 10 vertices (call it
TEMP)
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Use Reformat - Convert to convert this vector file to ASCII.
Then use notepad to open the TEMP.VEC file and copy and paste the coordinates
into your Word processing software to supplement your answer to the above
question.
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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).
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Import COUNTRY.SHP and rasterize the polygons to an image
called COUNTRY
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Use EXTRACT to find the average rainfall for each country.
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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).
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Use SCALAR to add 1 to MAYOCTPR and NOVAPRPR and name the
outputs MAYOCT1 and NOVAPR1 respectively
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Why do we have to add one to MAYOCTPR and NOVAPRPR (but
especially NOVAPRPR)?
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Divide MAYOCT1 by NOVAPR1 and call the output RATIO. The
values in RATIO provide all the information required to create a Rainfall
Regime image.
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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
| |
Hemisphere
|
Rainfall
Regime
|
Northern
|
Southern
|
| Summer |
|
|
| Winter |
|
|
| Uniform |
|
|
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.
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Create a blank image called CHANGER using INITIAL. Use an
intial value of 1.
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Find the row number of the first row below the equator.
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Use UPDATE to change all of the pixels in the southern hemisphere
in CHANGER to -1.
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Use OVERLAY to multiply RATIO and CHANGER to create a new
image called NSRATIO
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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.
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What are the minimum and maximum values of NSRATIO?
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RECLASS the NSRATIO image so that the Rainfall Regimes are classified with
the values described in Table 6.
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.
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What can you say about the distribution of summer, winter,
and uniform rainfall regimes in Africa?
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What do you notice along the equator? What causes this?
Can you think of a way to produce REGIMES without having this occur?
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Using Table 1 as a guide, RECLASS the images into boolean images called
ANNPRR, REGIMESR, MAXHOTR, MINCOLDR and ANNTMPR.
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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
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Use OVERLAY to create the final image called SUITABLE.
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Which OVERLAY operation should be used?
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Which country has the largest area of land suitable for
Eucalyptus? (HINT: Use EXTRACT).
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Use EXTRACT to see if the NDVI image derived from satellite data can distinguish
between rainfall regimes.
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Which statistic to you use for EXTRACT? Why?
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Is there a difference in NDVI statistics for the rainfall
regimes? Explain.
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Treat yourself to a beer or other preferred beverage.
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