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.

Motivation

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.

Spatial problems

General spatial problems are:

1. finding where something is,
   • we may not know the something we want to find explicitly, we may also just know something about it
2. network problems
   1. finding the best path between two known locations,
      • the "best" may also mean "at least one", and it can be interpreted as the shortest, fastest, most beautiful, etc
   2. more complex network problems, which involve visiting more than one location or more than one object moving in the network
3. finding the optimal location for something,
   • the "location" and the "something" may be a point, a line, or an area
4. (this is perhaps the most fundamental one) knowing where one is,
   • the location and orientation are not known, also knowing what is in one's neighborhood is a part of this problem
5. knowing what there is on some location,
6. are there others?

Spatial descriptions

When formulating spatial problems, we may need to formulate our knowledge or wishes also spatially. For example in problem (i), if we want to find a red car on an area, the problem is spatial only in the general sense, but if we want to find a red car which is on a parking lot, then also the description of what we want to find is spatial, in this case a spatial association between two spatial objects.

Spatial descriptions are attributes and associations of spatial objects or locations. Spatial descriptions of objects (or associated objects) may describe shape, orientation, associations, amount, or patterns. Spatial descriptions of locations (or associated locations) may describe dimension (0,1,2), shape, orientation.

Map making

The general problem of map making is creating a representation of an area. The GIS divides this into two parts:

1. creating a database of geospatial data and
2. creating an image from this data.

The power of GIS is in this separation but also in the possibility to link the two parts into an interactive system.

The first part immediately raises the question: "what is on the area and how do the things that there are relate to each other?" because that is how we start developing a spatial database.

The second part raises the question: "what kind of image to create, i.e, how do we judge what kind of image is good?". The goodness of a map can be judged by (at least) functional grounds and by aesthetic grounds.

GIS tool categories

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