Using Open Source GIS

This is one of the three books identified by the Education and Curriculum Committee that should be written. The other books are Developing Geospatial Solutions using Open Source and Developing Web Mapping Solutions Using Open Source.

Approach for writing this book

Using the application categories from http://freegis.org we'll gather problems or use cases, maybe divide them into subproblems, and describe how they can be solved using the free tools.

The tools are GUI applications and, to a lesser degree, command line tools.

This book is about "how do I realize that I have ended up in a situation where software, a GIS tool, is useful, and how do I then take advantage of the tool to solve my problem?".

Question: who might I be?

• Somebody with a new gadget X (GPS,...)
• Civil servant having to plan something with a spatial dimension
• Business analyst thinking about locations of shops and customers etc.

Describe these situations: possible situations are:

• somebody/something gives me a bunch of data, which I need to convert into
  • something else (but a bunch of data)
  • a map or a visualization or a document for human purpose in general
• I have a bunch of data and I want to
  • edit it because I know there are errors or things missing
• I need to find data for a specific purpose
• I need to plan or design something with a spatial dimension

What does "taking advantage" comprise: download, install, set up, work

It's important to understand that software tools are usually, and off-the-web tools always, designed to solve some technical problem(s) and the skill of using software is linking my problem to the problem that the software solves and then overcoming that link. Both of the problems have to be understood first of course. With GIS the skill may involve understanding how a certain real-world problem is conceptualized as something general spatial problem for which a solution exists.

General spatial problems are: (i) finding where something is, (ii) finding the best path between two known locations, (iii) finding the optimal location for something, (iv) (this is perhaps the most fundamental one) knowing where one is, (v) knowing what there is on some location, and are there others? In the first problem we may not know the something we want to find explicitly, we may also just know something about it. In the second problem the "best" may also mean "at least one", and it can be interpreted as the shortest, fastest, most beautiful, etc. In the third problem the "something" may be a point, a line, or an area. In the fourth problem the location and orientation are not known, also knowing what is in one's neighborhood is a part of this problem.

The general problem of map making is creating a representation of an area. The GIS divides this into two parts: (i) creating a database of geospatial data and (ii) creating an image from this data. The power of GIS is in this separation but also in the possibility to link the two parts in an interactive system. The first part immediately raises the question: "what is on the area and how is it connected?". The second part raises the question: "what kind of image to create, i.e, how do we judge what kind of image is good?". This question is strangely rarely (AFAIK) asked in cartography.

These are the categories:

• Misc/Fun
• Visualisation
• Interactive Viewing
• Web Mapping
• File-Format-Conversion
• GPS
• Base GIS
• Projection-Conversion
• Remote Sensing
• Customizable with Add-ons
• Flights
• SDI Management
• Mobile Geocomputing

Editing geospatial data

• Problem: Editing shapefile
  • Subproblem: Add or delete a feature
  • A solution:
  • Subproblem: Change the location of the vertices
  • A solution:
  • Subproblem: Edit attribute data
  • A solution:
  • Subproblem: Alter the schema (add or delete fields)
  • A solution:

Geocomputation

• Problem: Compute the total area of polygons in a dataset