# [QGIS Commit] r11063 - docs/trunk/english_us/gis_introduction

svn_qgis at osgeo.org svn_qgis at osgeo.org
Tue Jul 14 05:04:28 EDT 2009

Author: dassau
Date: 2009-07-14 05:04:28 -0400 (Tue, 14 Jul 2009)
New Revision: 11063

Modified:
docs/trunk/english_us/gis_introduction/Makefile
docs/trunk/english_us/gis_introduction/attributedata.tex
docs/trunk/english_us/gis_introduction/authors.tex
docs/trunk/english_us/gis_introduction/crs.tex
docs/trunk/english_us/gis_introduction/datacapture.tex
docs/trunk/english_us/gis_introduction/gis_introduction.tex
docs/trunk/english_us/gis_introduction/gisintro.tex
docs/trunk/english_us/gis_introduction/mapproduction.tex
docs/trunk/english_us/gis_introduction/rasteranalysis.tex
docs/trunk/english_us/gis_introduction/rasterdata.tex
docs/trunk/english_us/gis_introduction/topology.tex
docs/trunk/english_us/gis_introduction/vectoranalysis.tex
docs/trunk/english_us/gis_introduction/vectordata.tex
Log:
finished migration to latex

Modified: docs/trunk/english_us/gis_introduction/Makefile
===================================================================
--- docs/trunk/english_us/gis_introduction/Makefile	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/Makefile	2009-07-14 09:04:28 UTC (rev 11063)
@@ -21,8 +21,8 @@
make pics
latex $(FILE) #bibtex$(FILE)
-	bibtex $(FILE)1 - bibtex$(FILE)2
+	#bibtex $(FILE)1 + #bibtex$(FILE)2
#now loop over Latex files, until stable:
echo Rerun > $(FILE).log while grep Rerun$(FILE).log >/dev/null 2>&1 ; do latex $(FILE).tex ; done @@ -30,7 +30,7 @@ text: latex$(FILE)
-	bibtex $(FILE) + #bibtex$(FILE)
#now loop over Latex files, until stable:
echo Rerun > $(FILE).log while grep Rerun$(FILE).log >/dev/null 2>&1 ; do latex \$(FILE).tex ; done

Modified: docs/trunk/english_us/gis_introduction/attributedata.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/attributedata.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/attributedata.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,7 +15,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

If every line on a map was the same colour, width, thickness, and had the
same label, it would be very hard to make out what was going on. The map

Modified: docs/trunk/english_us/gis_introduction/authors.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/authors.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/authors.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -12,68 +12,65 @@
%\updatedisclaimer

\begin{figure}[ht]
-\centering
+\begin{center}
\begin{minipage}[h]{5cm}\includegraphics[width=4.7cm]{tim_sutton}
\end{minipage}
-\begin{minipage}[h]{11cm}
+\begin{minipage}[h]{11.5cm}
\textbf{Tim Sutton - Editor \& Lead Author} \\
Tim Sutton is a developer and project steering committee member of the
Quantum GIS project. He is passionate about seeing GIS being Freely available
to everyone. Tim is also a founding member of Linfiniti Consulting CC. - a
small business set up with the goal of helping people to learn and use open
source GIS software. \\
-\textbf{Web: http://linfiniti.com , Email: tim at linfiniti.com}
+Web: http://linfiniti.com , Email: tim at linfiniti.com
\end{minipage}
-\end{figure}

-\begin{figure}[ht]
-\centering
+\vspace{0.1cm}
+
\begin{minipage}[h]{5cm}\includegraphics[width=4.7cm]{otto_dassau}
\end{minipage}
-\begin{minipage}[h]{11cm}
+\begin{minipage}[h]{11.5cm}
\textbf{Otto Dassau - Assistant Author} \\
Otto Dassau is the documentation maintainer and project steering committee
member of the Quantum GIS project. Otto has considerable experience in using
and training people to use Free and Open Source GIS software. \\
-\textbf{Web: http://www.gbd-consult.de , Email: dassau at gbd-consult.de}
+Web: http://gbd-consult.de , Email: dassau at gbd-consult.de
\end{minipage}
-\end{figure}

-\begin{figure}[ht]
-\centering
+\vspace{0.1cm}
+
\begin{minipage}[h]{5cm}\includegraphics[width=4.7cm]{marcelle_sutton}
\end{minipage}
-\begin{minipage}[h]{11cm}
+\begin{minipage}[h]{11.5cm}
\textbf{Marcelle Sutton - Project Manager} \\
Marcelle Sutton studied english and drama and is a qualified teacher.
Marcelle is also a founding member of Linfiniti Consulting CC. - a
small business set up with the goal of helping people to learn and use open
source GIS software. \\
-\textbf{Web: http://linfiniti.com , Email: marcelle at linfiniti.com}
+Web: http://linfiniti.com , Email: marcelle at linfiniti.com
\end{minipage}
-\end{figure}

-\begin{figure}[ht]
-\centering
+\vspace{0.1cm}
+
\begin{minipage}[h]{5cm}\includegraphics[width=4.7cm]{lerato_nsibande}
\end{minipage}
-\begin{minipage}[h]{11cm}
+\begin{minipage}[h]{11.5cm}
\textbf{Lerato Nsibande} \\
Lerato is a grade 12 scholar living in Pretoria. Lerato learns Geography at
school and has enjoyed learning GIS with us!
\end{minipage}
-\end{figure}

-\begin{figure}[ht]
-\centering
+\vspace{0.1cm}
+
\begin{minipage}[h]{5cm}\includegraphics[width=4.7cm]{sibongile_mthombeni}
\end{minipage}
-\begin{minipage}[h]{11cm}
+\begin{minipage}[h]{11.5cm}
\textbf{Sibongile Mthombeni} \\
Sibongile lives near Johannesburg with her young daughter. Her goal is to
continue her studies and become a nurse. Working on this project was the
first time Sibongile used a computer.
\end{minipage}
+\end{center}
\end{figure}

Modified: docs/trunk/english_us/gis_introduction/crs.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/crs.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/crs.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,7 +15,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

\textbf{Map projections} try to portray the surface of the earth or a portion of the
earth on a flat piece of paper or computer screen. A \textbf{coordinate reference

Modified: docs/trunk/english_us/gis_introduction/datacapture.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/datacapture.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/datacapture.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -14,7 +14,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

In the previous two topics we looked at vector data. We saw that there are
two key concepts to vector data, namely: \textbf{geometry} and

Modified: docs/trunk/english_us/gis_introduction/gis_introduction.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/gis_introduction.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/gis_introduction.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -22,7 +22,7 @@
\include{rasteranalysis}
\include{authors}
\include{appendices/fdl}
-\include{literature}
+%\include{literature}

\begin{htmlonly}
\input{qgis_style.tex}

Modified: docs/trunk/english_us/gis_introduction/gisintro.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/gisintro.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/gisintro.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -20,7 +20,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

Just as we use a word processor to write documents and deal with words on a
computer, we can use a \textbf{GIS application} to deal with \textbf{spatial

Modified: docs/trunk/english_us/gis_introduction/mapproduction.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/mapproduction.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/mapproduction.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,7 +15,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

\textbf{Map production} is the process of arranging map elements on a sheet of paper
in a way that, even without many words, the average person can understand

Modified: docs/trunk/english_us/gis_introduction/rasteranalysis.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/rasteranalysis.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/rasteranalysis.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,6 +15,243 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

+\textbf{Spatial analysis} is the process of manipulating spatial information
+to extract
+new information and meaning from the original data. Usually spatial analysis
+is carried out with a Geographic Information System (GIS). A GIS usually
+provides spatial analysis tools for calculating feature statistics and
+carrying out  geoprocessing activities as data interpolation.
+In hydrology, users will likely emphasize the importance of terrain analysis
+and hydrological modelling (modelling the movement of water over and in the
+earth). In wildlife management, users are interested in analytical functions
+dealing with wildlife point locations and their relationship to the
+environment. Each user will have different things they are interested in
+depending on the kind of work they do.

+\subsection{Spatial interpolation in detail}
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Temperature map interpolated from South African Weather Stations.}
+\label{fig:temperature}\smallskip
+   \includegraphics[clip=true, width=0.5\textwidth]{temperatures_20090415}
+\end{center}
+\end{figure}
+
+\textbf{Spatial interpolation} is the process of using points with known values to
+estimate values at other unknown points. For example, to make a precipitation
+(rainfall) map for your country, you will not find enough evenly spread
+weather stations to cover the entire region. Spatial interpolation can
+estimate the temperatures at locations without recorded data by using known
+temperature readings at nearby weather stations (see Figure
+\ref{fig:temperature}). This type of interpolated surface is often called a
+\textbf{statistical surface}.
+Elevation data, precipitation, snow accumulation, water table and population
+density are other types of data that can be computed using interpolation.
+
+Because of high cost and limited resources, data collection is usually
+conducted only in a limited number of selected point locations. In GIS,
+spatial interpolation of these points can be applied to create a raster
+surface with estimates made for all raster cells.
+
+In order to generate a continuous map, for example, a digital elevation map
+from elevation points measured with a GPS device, a suitable interpolation
+method has to be used to optimally estimate the values at those locations
+where no samples or measurements were taken. The results of the interpolation
+analysis can then be used for analyses that cover the whole area and for
+modelling.
+
+There are many interpolation methods. In this introduction we will present
+two widely used interpolation methods called \textbf{Inverse Distance
+Weighting} (IDW) and \textbf{Triangulated Irregular Networks (TIN)}. If you
+interpolation methods, please refer to the further reading section at the end
+of this topic.
+
+\subsection{Inverse Distance Weighted (IDW)}
+
+In the IDW interpolation method, the sample points are weighted during
+interpolation such that the influence of one point relative to another
+declines with distance from the unknown point you want to create (see
+Figure \ref{fig:idw}).
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Inverse Distance Weighted interpolation based on weighted sample
+point distance (left). Interpolated IDW surface from elevation vector points
+(right). Image Source: Mitas, L., Mitasova, H. (1999).}
+\label{fig:idw}\smallskip
+   \includegraphics[clip=true, width=0.6\textwidth]{interpolation_IDW}
+\end{center}
+\end{figure}
+
+Weighting is assigned to sample points through the use of a weighting
+coefficient that controls how the weighting influence will drop off as the
+distance from new point increases. The greater the weighting coefficient, the
+less the effect points will have if they are far from the unknown point
+during the interpolation process. As the coefficient increases, the value of
+the unknown point approaches the value of the nearest observational point.
+
+It is important to notice that the IDW interpolation method also has some
+disadvantages: The quality of the interpolation result can decrease, if the
+distribution of sample data points is uneven. Furthermore, maximum and
+minimum values in the interpolated surface can only occur at sample data
+points. This often results in small peaks and pits around the sample data
+points as shown in Figure \ref{fig:idw}.
+
+In GIS, interpolation results are usually shown as a 2 dimensional raster
+layer. In Figure \ref{fig:qgisidw}, you can see a typical IDW interpolation
+result, based on elevation sample points collected in the field with a GPS
+device.
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{IDW interpolation result from irregularly collected elevation
+sample points (shown as black crosses).}
+\label{fig:qgisidw}\smallskip
+   \includegraphics[clip=true, width=0.6\textwidth]{qgis_interpolation_IDW}
+\end{center}
+\end{figure}
+
+\subsection{Triangulated Irregular Network (TIN)}
+
+TIN interpolation is another popular tool in GIS. A common TIN algorithm is
+called \textbf{Delaunay} triangulation. It tries to create a surface formed by
+triangles of nearest neighbour points. To do this, circumcircles around
+selected sample points are created and their intersections are connected to a
+network of non overlapping and as compact as possible triangles (see Figure
+\ref{fig:tin}).
+
+%% Minipage to put both figures on one page
+\begin{figure}[htpb]
+   \begin{minipage}[h]{\textwidth}
+   \begin{center}
+   \caption{Delaunay triangulation with circumcircles around the red sample
+data. The resulting interpolated TIN surface created from elevation vector
+points is shown on the right. Image Source: Mitas, L., Mitasova, H. (1999).}
+   \label{fig:tin}\smallskip
+   \includegraphics[clip=true, width=0.8\textwidth]{interpolation_TIN}
+   \end{center}
+   \end{minipage} \\
+   \vspace{1cm}
+   \begin{minipage}[h]{\textwidth}
+   \begin{center}
+   \caption{Delaunay TIN interpolation result from irregularly collected
+rainfall sample points (blue circles).}
+   \label{fig:qgistin}\smallskip
+   \includegraphics[clip=true, width=0.8\textwidth]{qgis_interpolation_TIN}
+   \end{center}
+   \end{minipage}
+\end{figure}
+
+The main disadvantage of the TIN interpolation is that the surfaces are not
+smooth and may give a jagged appearance. This is caused by discontinuous
+slopes at the triangle edges and sample data points. In addition,
+triangulation is generally not suitable for extrapolation beyond the area
+with collected sample data points (see Figure \ref{fig:qgistin}).
+
+\subsection{Common problems / things to be aware of}
+
+It is important to remember that there is no single interpolation method that
+can be applied to all situations. Some are more exact and useful than others
+but take longer to calculate. They all have advantages and disadvantages. In
+practice, selection of a particular interpolation method should depend upon
+the sample data, the type of surfaces to be generated and tolerance of
+estimation errors. Generally, a three step procedure is recommended:
+
+\begin{enumerate}
+\item Evaluate the sample data. Do this to get an idea on how data are
+distributed in the area, as this may provide hints on which interpolation
+method to use.
+\item Apply an interpolation method which is most suitable to both the sample
+data and the study objectives. When you are in doubt, try several methods, if
+available.
+\item Compare the results and find the best result and the most suitable method.
+This may look like a time consuming process at the beginning. However, as you
+gain experience and knowledge of different interpolation methods, the time
+required for generating the most suitable surface will be greatly reduced.
+\end{enumerate}
+
+\subsection{Other interpolation methods}
+
+Although we concentrated on IDW and TIN interpolation methods in this
+worksheet, there are more spatial interpolation methods provided in GIS, such
+as Regularized Splines with Tension (RST), Kriging or Trend Surface
+
+\subsection{What have we learned?}
+
+Let's wrap up what we covered in this worksheet:
+
+\begin{itemize}
+\item \textbf{Interpolation} uses vector points with known values to estimate
+values at unknown locations to create a raster surface covering an entire area.
+\item The interpolation result is typically a \textbf{raster} layer.
+\item It is important to \textbf{find a suitable interpolation method} to
+optimally estimate values for unknown locations.
+\item \textbf{IDW interpolation} gives weights to sample points, such that
+the influence of one point on another declines with distance from the new
+point being estimated.
+\item \textbf{TIN interpolation} uses sample points to create a surface
+formed by triangles based on nearest neighbour point information.
+\end{itemize}
+
+\subsection{Now you try!}
+
+Here are some ideas for you to try with your learners:
+
+\begin{itemize}
+\item The Department of Agriculture plans to cultivate new land in your area but
+apart from the character of the soils, they want to know if the rainfall is
+sufficient for a good harvest. All the information they have available comes
+from a few weather stations around the area. Create an interpolated surface
+with your learners that shows which areas are likely to receive the highest
+rainfall.
+\item The tourist office wants to publish information about the weather conditions
+in January and February. They have temperature, rainfall and wind strength
+data and ask you to interpolate their data to estimate places where tourists
+will probably have optimal weather conditions with mild temperatures, no
+rainfall and little wind strength. Can you identify the areas in your region
+that meet these criteria?
+\end{itemize}
+
+
+If you don't have a computer available, you can use a toposheet and a ruler
+to estimate elevation values between contour lines or rainfall values between
+fictional weather stations. For example, if rainfall at weather station A is
+50 mm per month and at weather station B it is 90 mm, you can estimate, that
+the rainfall at half the distance between weather station A and B is 70 mm.
+
+
+\textbf{Books}:
+
+\begin{itemize}
+\item Chang, Kang-Tsung (2006): Introduction to Geographic Information Systems. 3rd
+Edition.  McGraw Hill. (ISBN 0070658986)
+\item DeMers, Michael N. (2005): Fundamentals of Geographic Information Systems.
+3rd Edition. Wiley. (ISBN 9814126195)
+\item Mitas, L., Mitasova, H. (1999): Spatial Interpolation. In: P.Longley, M.F.
+Goodchild, D.J. Maguire, D.W.Rhind (Eds.), Geographical Information Systems:
+Principles, Techniques, Management and Applications, Wiley.
+\end{itemize}
+
+\textbf{Websites}:
+
+\url{http://en.wikipedia.org/wiki/Interpolation} \\
+\url{http://en.wikipedia.org/wiki/Delaunay\_triangulation} \\
+\url{http://www.agt.bme.hu/public_e/funcint/funcint.html}
+
+The QGIS User Guide also has more detailed information on interpolation tools
+provided in QGIS.
+
+\subsection{What's next?}
+
+This is the final worksheet in this series. We encourage you to explore QGIS
+and use the QGIS manual to discover all the other things you can
+do with GIS software!
+
+

Modified: docs/trunk/english_us/gis_introduction/rasterdata.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/rasterdata.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/rasterdata.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -14,7 +14,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

In the previous topics we have taken a closer look at vector data. While
vector features use geometry (points, polylines and polygons) to represent

Modified: docs/trunk/english_us/gis_introduction/topology.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/topology.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/topology.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,7 +15,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

\textbf{Topology} expresses the spatial relationships between connecting or

Modified: docs/trunk/english_us/gis_introduction/vectoranalysis.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/vectoranalysis.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/vectoranalysis.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,9 +15,275 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

+\textbf{Spatial analysis} uses spatial information to extract new and additional
+meaning from GIS data. Usually spatial analysis is carried out using a GIS
+Application. GIS Applications normally have spatial analysis tools for
+feature statistics (e.g. how many vertices make up this polyline?) or
+geoprocessing such as feature buffering. The types of spatial analysis that
+are used vary according to subject areas. People working in water management
+and research (hydrology) will most likely be interested in analysing terrain
+and modelling water as it moves across it.  In wildlife management users are
+interested in analytical functions that deal with wildlife point locations
+and their relationship to the environment. In this topic we will discuss
+buffering as an example of a useful spatial analysis that can be carried out
+with vector data.

+\subsection{Buffering in detail}

+\textbf{Buffering} usually creates two areas: one area that is
+\textbf{within} a specified distance to selected real world features and the
+other area that is \textbf{beyond}. The area that is within the specified
+distance is called the \textbf{buffer zone}.

+\begin{figure}[ht]
+   \begin{center}
+   \caption{The border between the United States of America and Mexico is
+separated by a buffer zone. (Photo taken by SGT Jim Greenhill 2006).}
+\label{fig:mexborder}\smallskip
+   \includegraphics[clip=true, width=0.6\textwidth]{border_usa_mexico}
+\end{center}
+\end{figure}

+A \textbf{buffer zone} is any area that serves the purpose of keeping real world
+features distant from one another. Buffer zones are often set up to protect
+the environment, protect residential and commercial zones from industrial
+accidents or natural disasters, or to prevent violence. Common types of
+buffer zones may be greenbelts between residential and
+commercial areas, border zones between countries (see Figure
+\ref{fig:mexborder}), noise protection zones around airports, or pollution
+protection zones along rivers.
+
+\newpage
+
+In a GIS Application, \textbf{buffer zones} are always represented as
+\textbf{vector polygons} enclosing other polygon, line or point features (see
+Figures \ref{fig:buffer}a-c).
+
+\begin{figure}[ht]
+\centering
+\caption{Buffering vector points, polylines and polygons}\label{fig:buffer}
+   \subfigure[A buffer zone around vector points.]
+   {\label{subfig:poibuffer}\includegraphics[clip=true, width=0.3\textwidth]{pointbuffer}}\goodgap
+   \subfigure[A buffer zone around vector polylines.]
+    {\label{subfig:linebuffer}\includegraphics[clip=true, width=0.3\textwidth]{polylinebuffer}}\goodgap
+   \subfigure[A buffer zone around vector polygons]
+    {\label{subfig:polybuffer}\includegraphics[clip=true, width=0.3\textwidth]{polygonebuffer}}
+\end{figure}
+
+\subsection{Variations in buffering}
+
+There are several variations in buffering. The \textbf{buffer distance} or
+buffer size \textbf{can vary} according to numerical values provided in the
+vector layer attribute
+table for each feature. The numerical values have to be defined in map units
+according to the Coordinate Reference System (CRS) used with the data.  For
+example, the width of a buffer zone along the banks of a river can vary
+depending on the intensity of the adjacent land use. For intensive
+cultivation the buffer distance may be bigger than for organic farming (see
+Figure \ref{fig:riverbuffer} and Table \ref{tab:buffer}).
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Buffering rivers with different buffer distances.}
+\label{fig:riverbuffer}\smallskip
+   \includegraphics[clip=true, width=0.5\textwidth]{variable_buffer}
+\end{center}
+\end{figure}
+
+%% Note: xdvi does not show white text on black background but it works!
+\begin{table}[ht]
+\centering
+\caption{Attribute table with different buffer distances to rivers based on
+ \label{tab:buffer}
+ \begin{tabular}{|p{5cm}|p{6cm}|p{5cm}|}
+ \hline
+ \rowcolor{black}
+ \textcolor{white}{\textbf{River}} &
+ \textcolor{white}{\textbf{Buffer distance (meters)}} \\
+ \hline Breede river & Intensive vegetable cultivation & 100 \\
+ \hline Komati & Intensive cotton cultivation & 150 \\
+ \hline Oranje & Organic farming & 50 \\
+ \hline Telle river & Organic farming & 50 \\
+\hline
+\end{tabular}
+\end{table}
+
+Buffers around polyline features, such as rivers or roads, do not have to be
+on both sides of the lines. They can be on either the left side or the right
+side of the line feature. In these cases the left or right side is determined
+by the direction from the starting point to the end point of line during
+digitising.
+
+\subsection{Multiple buffer zones}
+
+A feature can also have more than one buffer zone. A nuclear power plant may
+be buffered with distances of 10, 15, 25 and 30 km, thus forming multiple
+rings around the plant as part of an evacuation plan (see Figure
+\ref{fig:powerplant}).
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Buffering a point feature with distances of 10, 15, 25 and 30 km.}
+\label{fig:powerplant}\smallskip
+   \includegraphics[clip=true, width=0.4\textwidth]{multiple_buffer}
+\end{center}
+\end{figure}
+
+\subsection{Buffering with intact or dissolved boundaries}
+
+Buffer zones often have dissolved boundaries so that there are no overlapping
+areas between the buffer zones. In some cases though, it may also be useful
+for boundaries of buffer zones to remain intact, so that each buffer zone is
+a separate polygon and you can identify the overlapping areas (see Figure
+\ref{fig:buffertypes}).
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Buffer zones with dissolved (left) and with intact boundaries
+(right) showing overlapping areas.}
+\label{fig:buffertypes}\smallskip
+   \includegraphics[clip=true, width=0.9\textwidth]{dissolved_intact_buffer}
+\end{center}
+\end{figure}
+
+\subsection{Buffering outward and inward}
+
+Buffer zones around polygon features are usually extended outward from a
+polygon boundary but it is also possible to create a buffer zone inward from
+a polygon boundary. Say, for example, the Department of Tourism wants to plan
+a new road around Robben Island and environmental laws require that the road
+is at least 200 meters inward from the coast line. They could use an inward
+buffer to find the 200m line inland and then plan their road not to go beyond
+that line.
+
+\subsection{Common problems / things to be aware of}
+
+Most GIS Applications offer buffer creation as an analysis tool, but the
+options for creating buffers can vary. For example, not all GIS Applications
+allow you to buffer on either the left side or the right side of a line
+feature, to dissolve the boundaries of buffer zones or to buffer inward from
+a polygon boundary.
+
+A buffer distance always has to be defined as a whole number
+(\textbf{integer}) or a decimal number (\textbf{floating point value}). This
+value is defined in \textbf{map units} (meters, feet, decimal degrees)
+according to the Coordinate Reference System (CRS) of the vector layer.
+
+\subsection{More spatial analysis tools}
+
+Buffering is a an important and often used spatial analysis tool but there
+are many others that can be used in a GIS and explored by the user.
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Spatial overlay with two input vector layers (a\_input =
+rectangle, b\_input = circle). The resulting vector layer is displayed
+green.}
+\label{fig:overlay}\smallskip
+   \includegraphics[clip=true, width=\textwidth]{overlay}
+\end{center}
+\end{figure}
+
+\textbf{Spatial overlay} is a process that allows you to identify the relationships
+between two polygon features that share all or part of the same area. The
+output vector layer is a combination of the input features information (see
+Figure \ref{fig:overlay}). Typical spatial overlay examples are:
+
+\begin{itemize}
+\item \textbf{Intersection}: The output layer contains all areas where both
+layers overlap (intersect).
+\item \textbf{Union}: the output layer contains all areas of the two input
+layers combined.
+\item \textbf{Symmetrical difference}: The output layer contains all areas of
+the input layers except those areas where the two layers overlap (intersect).
+\item \textbf{Difference}: The output layer contains all areas of the first
+input layer that do not overlap (intersect) with the second input layer.
+\end{itemize}
+
+\subsection{What have we learned?}
+
+Let's wrap up what we covered in this worksheet:
+
+\begin{itemize}
+\item \textbf{Buffer zones} describe areas around real world features.
+\item Buffer zones are always \textbf{vector polygons}.
+\item A feature can have \textbf{multiple} buffer zones.
+\item The size of a buffer zone is defined by a \textbf{buffer distance}.
+\item A buffer distance has to be an \textbf{integer} or \textbf{floating
+point} value.
+\item A buffer distance can be different for each feature within a vector layer.
+\item Polygons can be buffered \textbf{inward} or \textbf{outward} from the
+polygon boundary.
+\item Buffer zones can be created with \textbf{intact} or \textbf{dissolved}
+boundaries.
+\item Besides buffering, a GIS usually provides a variety of vector analysis tools
+\end{itemize}
+
+\subsection{Now you try!}
+
+\begin{itemize}
+\item Because of dramatic traffic increase, the town planners want to widen the
+properties that fall within the buffer zone (see Figure \ref{fig:lanebuffer}).
+\item For controlling protesting groups, the police want to establish a neutral
+zone to keep protesters at least 100 meters from a building. Create a buffer
+around a building and colour it so that event planners can see where the
+buffer area is.
+\item A truck factory plans to expand. The siting criteria stipulate that a
+potential site must be within 1 km of a heavy-duty road. Create a buffer
+along a main road so that you can see where potential sites are.
+\item Imagine that the city wants to introduce a law stipulating that no bottle
+stores may be within a 1000 meter buffer zone of a school or a church. Create
+a 1km buffer around your school and then go and see if there would be any
+bottle stores too close to your school.
+\end{itemize}
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Buffer zone (green) around a roads map (brown). You can see which
+houses fall within the buffer zone, so now you could contact the owner and
+talk to him about the situation.}
+\label{fig:lanebuffer}\smallskip
+\end{center}
+\end{figure}
+
+
+If you don't have a computer available, you can use a toposheet and a compass
+to create buffer zones around buildings. Make small pencil marks at equal
+distance all along your feature using the compass, then connect the marks
+using a ruler!
+
+
+\textbf{Books}:
+
+\begin{itemize}
+\item Galati, Stephen R. (2006): Geographic Information Systems Demystified. Artech
+House Inc. (ISBN 158053533X)
+\item Chang, Kang-Tsung (2006): Introduction to Geographic Information Systems. 3rd
+Edition.  McGraw Hill. (ISBN 0070658986)
+\item DeMers, Michael N. (2005): Fundamentals of Geographic Information Systems.
+3rd Edition. Wiley. (ISBN 9814126195)
+\end{itemize}
+
+\textbf{Websites}:
+
+\url{http://www.manifold.net/doc/transform\_border_buffers.htm}
+
+The QGIS User Guide also has more detailed information on analysing vector
+data in QGIS.
+
+\subsection{What's next?}
+
+In the section that follows we will take a closer look at
+\textbf{interpolation} as an example of spatial analysis you can do with
+raster data.
+
+

Modified: docs/trunk/english_us/gis_introduction/vectordata.tex
===================================================================
--- docs/trunk/english_us/gis_introduction/vectordata.tex	2009-07-13 20:58:51 UTC (rev 11062)
+++ docs/trunk/english_us/gis_introduction/vectordata.tex	2009-07-14 09:04:28 UTC (rev 11063)
@@ -15,7 +15,7 @@
\hline
\end{tabular}

-\subsection{Overview}\label{subsec:overview}
+\subsection{Overview}

\textbf{Vector data} provide a way to represent real world \textbf{features}
within the GIS environment. A feature is anything you can see on the