How you ever wondered how maps are made?

1. Let's Try For U & Me
Map-Making
with QGIS ­Part—1
Have you ever wondered how maps are made? In this article, we will take our first step towards
making maps from spatial data using Quantum Geographic Information System (QGIS).
Q
GIS is one of the most
widely used open source
desktop tools for map-
making and basic GIS analysis.
You can download it from http://
download.qgis.org. QGIS is useful
for visualising and editing spatial
data, and for querying its features.
Features are the geographical objects
in the layer, e.g., each individual
airport is a feature in the airports
layer. A feature will have attributes
describing it, such as the geometry,
name, category, etc.
QGIS has a Map Composer,
which allows you to add the essential
map elements and get the map print- Figure 1: Alaska and Airports shapefiles
ready. QGIS comes with dozens
of handy plug-ins, and a Python
console, just in case developers want
to interact with the data through the
command interface. For this tutorial,
we will be using version 1.7.3 with
the Alaska dataset available at http://
download.osgeo.org/qgis/data/qgis_
sample_data.zip.
Visualise shapefiles
QGIS supports most common vector
file formats—Shapefile, KML,
GML, GPX, etc. The procedure to
open the files is the same for all
formats:
1. On the menu, click Add Vector
Layer. Figure 2: Layer styles
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2. For U & Me Let's Try
2. Browse to the source (for our
example, the qgis_sample_data/
shapefiles directory).
3. Select the files (in our case, alaska.
shp and airports.shp). Figure 1
shows the Map Canvas with the
Alaska and Airports layers.
Layer styles
Styling allows us to set fill colours,
patterns, borders, icons, etc, for the
features in the layer:
1. Right click the Airport layer in the
Layers panel and select Properties.
2. Under the Style tab you can
change the symbol and colour,
the size of the symbol, set
transparency, and categorise the
features (see Figure 2).
Layer labels
Figure 3: Feature labels
Labels are text identifiers for features in
the layer. QGIS allows you to choose the
attribute you want to show as the label,
and set its style too (see Figure 3):
1. Right click the Airport layer and
select Properties.
2. Under the Labels tab, check mark
Display Labels.
3. Select the Field Containing Label; this
is the text to be shown on the layer.
4. Set the font size, colour, type, and
the text position with respect to the
feature location.
Attributes table
Attributes describe the features in
a layer. The attribute values can be
edited and queried. To view attribute
names and data, right click the Airport
layer and choose Open Attribute Table.
To query features of your interest,
add the text to filter the data in the Look Figure 4: Feature selection
For text box, and select the desired field.
For instance: look for ‘Military’ in the format as ESRI Shapefile and save. publish a map, plot custom data and
field ‘Cat’. Then hit Search. You will In Part II, we will learn how to perform geoprocessing.
find that all military airports are selected
and highlighted in the Attribute Table, By: Sagar Arlekar & Niket Narang
as in Figure 4, and on the map. For The authors are researchers at the Center for Study of Science, Technology
complex queries, try Advanced Search. and Policy (CSTEP), Bengalore. They work in the fields of GIS and Agent-Based
Selected features can be saved as Simulation. At CSTEP they have built a web-based GIS framework to simulate and
visualize disaster impact. They love working with open source tools and are active
a new shapefile: click Layer > Save
contributors to Openstreetmaps.
Selection as vector file. Select the
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