This aim of this practical exercise is to expand the concepts introduced in the last practical exercise,
specifically in the areas of raster (grid cell) geographic and analysis. Students are introduced to the
concept of raster data in addition to common raster analysis functions. Students will also be
introduced to creating a geodatabase. At the completion of this exercise, students should have an
appreciation for the way in which raster data is stored and analysed within a GIS.
The data you will be using for this practical exercise is available from Blackboard (Course
Documents>Practical Exercises>Files for Prac 2). Save these files to your “H:” drive.
**Remember to use 7-zip to extract the data**
The submission for this practical exercise consists of written answers to questions 1 to 6. It is
expected that submissions will be no more than 2 pages in length. Submissions must be accompanied
by a School of Science cover sheet and should be submitted via the assignment drop box in Building
3, level 1, room 2 (reception) or the Engineering Academic Services Centre assignment drop box in
Building 10, level 9.
This practical assignment is due 1 week after the completion of the practical project.
GEOM1033 & GEOM1159 SIS Fundamentals & GIS Fundamentals
Practical Project 2: Raster Geographic Data and Analysis
A Simple Raster GIS Project and Geodatabase Creation
We will explore some of the fundamental operations of a raster GIS. Two of these fundamental
operations are (i) Map Algebra and (ii) Zone analysis. We will also create a file geodatabase, which is
a family of formats that allows for more flexibility with a variety of data types and for optimised
1) If you have not done so already, copy the directory available from Blackboard (Course
Documents>Practical Exercises>Files for Prac 2) to your work area on your “H: drive”.
**Remember to use 7-zip to extract the data**
2) Open a new (blank) ArcMap™ document (File>New).
3) In ArcCatalog (within ArcMap) navigate to the directory where you copied the data for this project.
Remember, you might need to use the “Connect to Folder” button.
4) Right mouse click and create a new geodatabase: New>file geodatabase at the folder level.
5) Rename your geodatabase to something more meaningful (eg. Sorghum_Geodatabase.gdb).
6) Now import the two grid files into your geodatabase. To do this, right mouse click over your
geodatabase file in the ArcCatalog window and select “Import Raster datasets”, and then select
the two raster files. Leave “Configuration Keyword” blank. Click “OK”.
7) You can now add your geodatabase to the ArcMap project and select the two raster files.
8) We will now set this new geodatabase to be the default geodatabase for this project, so that all
outputs will be automatically directed into it. Right mouse click over your new geodatabase in
ArcCatalog and select “Make Default Geodatabase”.
9) Right mouse click over the SG_DEM raster layer and select properties>symbology and in the
“show” window select “Unique Values”. Build the attribute table when prompted. Change the
symbology to something appropriate for the display of elevation data (hint – select one of the
colour schemes from the bottom of the colour schemes drop down list on the symbology tab of
the layer properties dialog).
10) Use the Identify tool to query cell values at different locations.
Question 1
What information do the “value” and “count” fields contain? What could we interpret about a raster
layer if the all of the count values were equal to 1?
This grid (raster layer) is a digital elevation model (DEM) of an area along the Senegal River in
Mauritania. The area to the south of the river is not included in the analysis as it is in Senegal. This
area is subject to flooding each year during the rainy season. Since the area is normally very dry,
local farmers practice what is known as “recessional agriculture” by planting in the flooded areas after
the waters recede. The crop that is normally grown in this fashion is the cereal crop sorghum.
GEOM1033 & GEOM1159 SIS Fundamentals & GIS Fundamentals
Practical Project 2: Raster Geographic Data and Analysis
A project has been proposed to place a dam along the north bank at the northern most part of the
bend in this river. The intention is to let the flood waters enter this area as usual, but then raise a dam
to hold the waters in place for a longer period of time. This would allow more water to soak into the
soil, increasing sorghum yields. The annual flood level is nine metres above normal river height.
In addition to water availability, soil type is an important consideration in sorghum agriculture because
some soils retain moisture better than others. In this area only clay soil is suitable for this kind of
agriculture. The aim of the project is to determine how many hectares of land are suitable for sorghum
agriculture. Below is a flow chart of the cartographic modelling (map algebra) process needed to
complete the project.
11) Determine the maximum and minimum elevation values for the SG_DEM grid (hint – use the
source tab from the layer properties dialog).
12) The first step in this project is to create a layer showing areas prone to flooding. Reclassify the
SG_DEM layer and call the output raster FLOOD. To do this open the ArcToolbox>Spatial Analyst
Tools>Reclass>Reclassify. Use the following data ranges for your reclassification. Ensure that
your file is correctly pathed to add the output to your geodatabase.
Assign a new value of: 1
To values from: 0 to 9
Assign a new value of: 0
To values from: 10 or more
Question 2
What do the values of “1” in the FLOOD raster layer represent? What is the reason that we use zero
for the rest of the original raster layer?
13) Use the information below to show the SG_SOILS raster layer to update the legend under “Label”
in Layer Properties>Symbology. Make sure you also change the colours for each type of soil to
something appropriate. You may need to select “unique” to show all individual values.
0 No Data
1 Heavy Clay
2 Clay
3 Sandy Clay
4 Levee Material
5 Stony Ground
14) We know that clay soil is the best for growing sorghum so we will now create a raster layer that
identifies only areas of clay soil. Reclassify the SG_SOILS layer using the following values and call
your output raster layer BestSoil:
Old Value New Value
0 0
1 0


Prime Essay Services , written from scratch, delivered on time, at affordable rates!