Appearance of interface:
Toolbar
buttons
Toolbar menu options
Displaying attribute values
Altering default colour scheme
Visualisation map tools:
Choropleth
maps
Standalone
bars
Graduated
circles
Pies
Triangles
Cross
classification
Visualisation chart tools:
Scatter
plot
Scatter
plot matrix
Query tools:
Dynamic
queries
Measuring distances
Calculation tools:
Sum
of columns
Percentages
and ratios
Change, difference
Toolbar buttons
Pan map
Use this tool to fit the map into the screen, i.e. after using the zooming
in and out tools, clicking on this button refreshes the original view
of the map.
Zoom in
Use this button to zoom in and see more detail on your map. It uses the
centre of the map as the zooming in point.
Zoom out
Use this button to zoom out. It uses the centre of the map as the zooming
out point.
Undo zoom
Using undo zoom undoes the last zooming action.
Drag zoom
Use this button to choose a specific area on the map to see in more detail.
Click the button and then use your mouse the drag and draw a rectangle
which will then fill the view.
Move map
Use this button to move around on your map. When the button is highlighted
use the mouse to drag and draw a straight line. The map moves in the same
direction and the same distance of the line - as though it is being pushed
along by the cursor.
Select objects
When this button is highlighted, objects (such as countries) on the map
can be selected either by clicking on them or dragging the cursor across
the screen. When selected an object appears with a black outline. Click
on object again to deselect.
Deselect all objects
Clicking on this button deselects all selected objects.
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Toolbar menu options
Under the Display toolbar menu option the following
choices are available:
Under the Calculate toolbar menu option the following
choices are available:
- Sum
of columns > Creates a new attribute based the sum of two existing
columns
- Percentages
and ratios > Creates a new attribute based on existing attribute
data using either percentage or ratio computations
- Change,
difference > Creates a new attribute based on existing attribute
data calculating the change or difference between two attributes
Under the Tools toolbar menu option the following choices
are available:
Under the Options toolbar menu option the following
choices are available:
- Show records options > Allows selection of objects on the map,
(e.g. countries) and to view specific associated attributes for each
of those selected objects.
- Verify relationship between variables > System asks before visualizing
combinations of attributes
- Warn of misuse
Under the Help toolbar menu option the following choices
are available:
- Index > Default CommonGIS Help pages
- About > Information about CommonGIS
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Displaying attribute
values
To display attribute values on a map, choose Display > Display
Wizard from the toolbar menu, select from the list of available attributes
and click OK. You will then be given a choice of visualisation
tools dependant on the number of attributes you have chosen to view.
For example if one attribute was selected the map options would be -
Unclassified and Classified choropleth maps,
Standalone bars and Graduated circles.
However, if more than one attribute was selected the map options would
differ - Pies, Triangles,
Cross-classification, Multiple
choropleth maps and there would also be a couple of chart visualisation
options - Scatter plot and Scatter
plot matrix.
By hovering over an object on a map, you can see the associated attribute
data. In the example below population attribute data has been added as an
unclassified choropleth map. By holding the mouse over Poland (a map object)
the value for the population
attribute of Poland is displayed.
Another way to view an object's attribute value is to use the side bar
to highlight the corresponding circle marker - see diagram below.
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Altering default colour
scheme
The colours used in CommonGIS can be customised by clicking onto the
Legend tab and then clicking onto the attribute colour key bar. The Colour
selection window will appear and both positive and negative colour
options can be changed.
Note: The Background colour of the display can also
be changed by clicking on the grey Background key.
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Choropleth maps
This cartographic visualisation technique involves displaying numeric
attribute values as colours or shades. Using this method it is easy to
compare and view the relationship of neighbouring objects.
CommonGIS supports three types of choropleth map; i) Unclassified,
ii) Classified and iii) Multiple.
Unclassified choropleth map
In an unclassified choropleth map the numeric attribute values are converted
directly into proportional degrees of darkness, i.e. the higher the object's
attribute value, the darker the shade representing it. The diagram below
shows the fertility rate attribute values for countries in Europe. The
maximum fertility rate is 2.27 children born per woman in Albania and
is represented by the darkest shade of orange and the minimum fertility
rate is 1.13 children born per woman in Bulgaria represented by the lightest
shade of orange.
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Dynamic midpoint and unclassified choropleth maps
To emphasize progression outward from a critical midpoint of data cartographers
often use a diverging colour scheme to differentiate visually the values
above and below that midpoint. Using CommonGIS it is possible to dynamically
change the midpoint of the data and observe corresponding changes to an
unclassified choropleth map.
To alter the critical mid point of the data tick the Dynamic map
update checkbox and move the double ended arrow on the attribute
side bar with mouse and observe the spatial patterns and trends.
Note: Another method of determining the critical
mid point is to type a figure directly into the Compare to input box.
In the example screen shots below infant mortality rate data is displayed
with a critical mid point of 35.77 (number of deaths of infants under
one year old in a given year per 1,000 live births). The countries shown
in orange/brown shades (Turkey, Moldova and Albania) are those countries
with an infant mortality rate higher than 35.77 and those in blue shades
have a lower rate.
As the arrow is moved down the side attribute bar, the spatial trends
of the data can be seen.
If the Compare by click in check box is ticked and you select
a country object on the Europe map, it will turn white and the value associated
with the selected country becomes the critical mid point reference value.
Country objects with higher values will be displayed in shades of brown,
and country objects with lower values in blue.
For example in the screen shot below the Compare by click in functionality
has been used to display how other countries in Europe compare to Italy's
infant mortality rate of 5.76 per 1000 live births.
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Classified choropleth map
In a classified choropleth map the value range of a numeric attribute
is divided into differently coloured intervals. The country objects are
therefore displayed on the map according to the interval their associated
attribute values fall into.
For example in the screen shot above showing Fertility rate figures for
Europe, those countries which fall into the lowest fertility band are
shown in dark blue and those with the highest rate are shown in dark red.
Methods of defining classes
The classes can be defined manually by moving the double ending arrows
on the attribute slide bar or by clicking on the slide bar to add another
interval.
The intervals of classes can also be altered by using the text editing
control which lists current values of the breaks, i.e. in the example
above the full range of the attribute value is 1.130 to 2.270 with interval
break values of 1.227, 1.408, 1.630 and 1.755. These break values can
be edited, removed or added to using the text editing control.
If you click on Automatic classifications you will see a number
of automatic classification options:
- Equal size classes
- Equal interval
- Nested means
- Optimal classification
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Multiple choropleth maps
The Multiple choropleth map visualisation method allows you to view a
number of attributes at the same time. After clicking on Display Wizard
> Display and choosing the attributes you wish to view, click
the Multiple choropleth maps check box and click OK.
The multiple choropleth map in the screen shot below shows Birth and
Death rates in Europe. The darkest blue shade in the top choropleth map
representing the Birth rate attribute shows Albania with the highest birth
rate of 18.59, with Turkey close behind with 17.95. The lower choropleth
map represents the Death rate attribute and shows Turkey with the darkest
orange shade has the lowest Death rate of 5.95.
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Standalone bars
The standalone bar tool allows visualisation of an attribute via a single
bar with a height proportional to the value.
In the example screen shot below the standalone bars have been manipulated
to allow comparison of Life expectancy rates in Europe by using the Compare
by click in tool. The critical mid point age of 75 has been typed
into the Compare to input box. The values shown in yellow shades
with an upwards extending bar are those countries that have a life expectancy
above 75 years. Whereas those displayed in blue shades with the bar extending
downwards identify countries with a life expectancy below 75 years.
Note: The height, width and color of the
bars can be altered using the Legend tab.
Graduated circles
The graduated circles tool allows visualisation of an attribute via a
circle with a diameter proportional to the value.
In the example screen shot below the graduated circles have been manipulated
to allow comparison of the percentage of 0-14 yr olds in Europe by using
the Compare by click in tool. Poland has been chosen as the country
to be compared with. It's population is made up of 17.9% of 0-14yr olds
- the value shown in the Compare to input box. The values shown
in red shades are those countries that have a greater percentage of their
population made up of 0-14yr olds whereas those displayed in blue shades
have a lower percentage. The lowest and highest attribute values are displayed
as the largest circles, i.e. Albania = 28.8% and Italy = 14.1%.
Note: The size and color of the circles
can be altered using the Legend tab.
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Pies
Pies allow you to visualise a number of related attributes to see proportions
and make meaningful summary pie charts. For example in the screen shot
below the age structure of countries population are displayed as pie charts.
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Triangles
Using the CommonGIS Triangles tool, two selected attributes can be visualised.
Which axis belongs to which attribute is shown in the legend part of
the screen on the right hand side by small double arrows. In the screen
shot below the vertical axis represents the percentage population growth
in Europe and the horizontal axis represents the Birth rate (average annual
number of births during a year per 1,000 persons).
As the crude birth rate is usually the dominant factor in determining
the rate of population growth, the triangle visualisation technique can
be used to identify any anomalies. These would be shown by either short
and fat triangles, i.e. low population growth but high crude birth rate
or tall and thin triangles, i.e. high population growth rate but low birth
rate.
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Cross classification
When choosing two attributes to visualise CommonGIS offers an option
Cross Classification.
In a cross classification map the value range of the numeric attributes
are plotted onto a scatter plot map which is divided into differently
coloured intervals. The country objects are therefore displayed on the
map according to the interval their associated attribute values fall into
The intervals or splits can be manually altered by using the Text input
box along the axis or by simply clicking on the attribute slide bar to
add another interval. The screen shot below shows the same key as above,
but with additional intervals.
To view just those items within a particular section of the scatter plot,
click on that square within the scatter plot and the associated map will
highlight only those countries selected - all others will be greyed out.
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Scatter plot
The scatter plot option is available when visualising two attributes.
After clicking on Display wizard and choosing your attributes,
select the cross classification and scatter plot check boxes.
The screen shot below shows the scatter plot for Birth rate and Population
growth rate and associated cross classification map. You can see that
the items selected by mouse dragging (shown in the pink box) are highlighted
with black boundary lines on the map of Europe.
To deselect selected items simply click elsewhere on the scatter plot
matrix.
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Scatter plot matrix
The scatter plot matrix is available when visualising two or more attributes
in CommonGIS. After clicking on Display Wizard and choosing your
attributes, tick the check box Scatter plot matrix and click
OK.
A square matrix will appear which has the names of the attributes positioned
in a diagonal line next to the scatter plots. The axes of the plots are
identified by the attribute entries displayed in the diagonal line.
For example in the example screen shot below two attributes Population
growth rate (%) and Net migration rate (per 1000) are shown along the
diagonal line. The position of these attribute headings shows that for
the plot shown on the top right of the image Population growth rate is
the Vertical attribute axis but for the plot shown at the bottom left
of the image the Population growth rate is the Horizontal attribute axis.
The plots can be manipulated in the same way as scatter
plots.
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Dynamic queries
With the CommonGIS dynamic query tool you can interactively set and dynamically
alter constraints on attribute values. The constraints set are then reflected
in the map which is immediately redrawn to show only those countries that
satisfy the constraints.
To use this tool click onto Tools > Dynamic Query from the
Toolbar menu.
In the Dynamic Query Window which appears select at least two
attributes and click OK. The two attributes are displayed as
sliding constraint bars, which can be used to set parameters for the objects
to be displayed. Next to each attribute constraint sliding bar there is
another bar which shows how many objects fulfil the constraints for that
attribute. The last bar on the right hand side shows how many objects
satisfy the constraints for all attributes.
For example in the screen shot below 14 countries from 38 satisfy the
constraint put on the Population growth rate (i.e. value between range
0.027 to 0.34), 26 countries out of 38 satisfy the constraint put on the
Death rate (i.e. value between range 9.3 to 16.4) and only 11 countries
from 38 satisfy the constraints imposed on both attributes.
The map associated with the attributes is dynamically updated, so for
example the constraints imposed on the country attributes above - Population
growth rate and Death rate result in the map displayed in
the screen shot below, i.e. where only 11 countries are now highlighted.
Note: If an object has no value assigned it can
be excluded from the resulting objects by activating the Filter out missing
values check box in the bottom left hand side of the Dynamic Query Window.
It will then not appear in the last statistic bar.
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Measuring distances
To access the measure distance tool, select Tools > Measure distances
from the Toolbar menu.
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Sum of columns
Using this tool, accessed through the Calculate option on the
menu toolbar, the selected attributes are summed up and a new attribute
is created.
A default name of the new attribute is provided, but can be edited. The
new attribute is then added to the database and displayed on the map by
degrees of darkness.
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Percentages and ratios
This tool allows you to create a new attribute based on existing attribute
data using either percentage or ratio computations. To access the tool
tick the Percentages and ratios check box after selecting Calculate
from the toolbar menu and choose one or more attributes.
Use the tool to calculate the percentage or ratio of attributes divided
by their sum, another attribute or a constant. After clicking OK,
another attribute is added to the database and will be available to add
to the map under Display > Display wizard.
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Change, difference
CommonGIS provides the change, difference tool accessible from the Calculate
option in the toolbar. It allows you to calculate either the change, ratio
or difference between two attribute values. The options are as follows:
- A - B
- A / B
- 100 * A / B
- (A-B) / B
- 100 * (A-B) / B
Note: The Invert button switches the attributes
A and B.
After clicking OK, another attribute is added to the database
and is displayed as an unclassified choropleth map.
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