The purpose of this exercise is to have you create spatial
data by digitizing points in Google Earth, and then do some
analysis of the point patterns in QGIS.
In QGIS, you will experiment with some of the spatial analytic
functions under the Vector menu drop downs...
In particular let's take a look at the degree of randomness in the point pattern. (See geographyfieldwork.com/nearest_neighbour_analysis.htm for some background on that.) We'll use Q's nearest neighbor index and interpret indices from 0.0 to about .75 indicate clustering; from .75 to 1.25 suggest randomness; and above 1.25 suggests regular spacing.
Materials. Access to QGIS, the internet, and a web browser.
The world is awash with GIS data available on the web. (See the list at the end of this document for some examples.) These data typically have spatial and attribute components and are provided in GIS-accessible formats such as ASCII text files, shapefiles, and other exchange formats. Some of these data are available through special purpose spatial data servers using specialized web clients (Google Earth is an example) to connect to online databases. Some are expressly in the public domain, and others have proprietary restrictions on their use. GIS data for distribution should come with metadata that describe the data and should help you assess whether the data are suitable for your intended use. Minimally, metadata should identify the coordinate system used for the spatial data and a data dictionary which tells what attributes are included and how they are encoded. Metadata might also include information on data provinence and assessments of its completeness and accuracy.
Google Earth is amazing for it's ability to provide imagery (and some vector data), but often one wants to record vector coordinates to represent features that one has interpreted from the imagery. Google Earth provides an easy way to do just that. With Google Earth you can capture and export geographic coordinates into .kml, an XML ascii text file format that can be ingested by a number of other GIS applications.
The steps are these:
Quantum GIS (QGIS) is a free and open source (FOSS) geographic information system (GIS) that is free; runs on MS-Windows, MacOS, and Linux; uses common data file formats; presents a 'typical' point-and-click interface; and provides sufficient spatial analytic capabilities to demonstrate several GIS functions. For this assignment, the data input, data selection and symbolization, and map output functions will be most relevant.
Download and install QGIS. QGIS can be downloaded from www.qgis.org .
Start the QGIS program. Take a few moments to see what is under each menu tab; the names may not make sense at first but reading through them now will make it easier to find things later.
Reading data into QGIS... Reading vector data is in the Menu: Layer -> Add Vector Layer ... (or an icon in the menu bar). In the panel dialog, you will need to navigate to a directory and specify a kind of file to show (e.g., [OGR] KML or SHAPEFILE). Tell it to load the data. You should see the data and an entry in the "TOC" to the left. Reading OSM data requires a plugin. See the section below.
Open the attribute table for your features to explore the data that you have. (Layer:Open Attribute Table) You should see that there are records in the table, for each feature on the map and that you can sort the records on the values in the various fields. You can use the query facility at the bottom of the table panel to select features.
You can export the map as an image file, maybe to add to a document. (File:Save as Image...)
You can set map symbology for your data. In the "TOC" you can check layers on and off, drag layers up and down in the "TOC" so that points and lines appear "on top of" polygons, and can change the colors and symbol sizes for features in layers. There are rudimentary classification tools to produce range-graded graduated color symbols. (Right click the layer in the TOC, choose Properties, then Symbology.)
CRS . When different layers of information are coming from (or are "in") different projections, or coordinate reference systems, you need to enable "on the fly" coordinate conversion, and may need to explicitly set the projection to use for the map display. (Use File:Project Properties:Coordinate Reference System (CRS) tab to select the desired coordinate system for the map display and "check" the "Enable 'on the fly' CRS transformation" if QGIS will need to re-project data sets.
Saving a snapshot of a map from QGIS... from the menu... File:Save as Image will let you save a .jpg (or .bmp etc.) image of the map from your screen which you could then include in a webpage or other document.
The order in the TOC sets the drawing order for layers. You can symbologize the content in each layer, setting line weights and colors (based on data values).
Reading a .kml file, or for that matter many different GIS vector file formats into QGIS is easy.
At this point, you should be able to work with the geometric and attribute data for your features.
You may want to add further attributes to the tabular data. (toggle editing in the table)
You may want (or even need) to separate point, line, and polygon features for further processing and export to other formats. (Right click the layer in the table of contents and select "Save as..."