Worksheet 1 Flashcards
who developed QGIS?
QGIS has been developed by an online user community and is free to download. It is frequently updated
but the version (3.28.13) we will use is the most recent ‘long term release
What is a long term release version?
’A long term release version
is the most recent stable version, newer versions such as 3.32 that you may encounter are being trialled
by experts and are not suitable for student learning, i.e. they are unstable.
GIS are modular systems, what does this mean?
It means that the core system is connected to multiple modules that can be
opened through the main window (browser or toolbox
The core system of GIS is like a spider connected to multiple modules that can be accessed through the main window (browser or toolbox). This complexity makes learning GIS tricky, but it provides great flexibility, allowing users to utilize only the desired features while ignoring other complicated app extensions.
What are the main features of GIS? (7)
- You can view combinations of vector and raster data (in 2D or 3D) in different formats and
projections - Explore data and compose maps
- Create, edit, manage and export vector and raster layers
- Perform spatial data analysis on spatial databases
- Publish maps on the Internet
- Extend QGIS functionality through plugins: QGIS can be adapted to your special needs by adding
external apps (termed plugins). - Python Console- This interface provides access to the mapping tools, menus, toolbars and other
parts of the QGIS application. More advanced use of QGIS, beyond second year, often requires
knowledge of the python language to automatic complex tasks.
What are the additional 2 features of QGIS
GRASS and GDAL
What is GRASS?
GRASS is an independent set of databases and GIS system accessible through QGIS.
GRASS GIS is a project developed by an international team since 1982, involving scientists, developers, and organizations. While not covered in this module, it’s a valuable tool for research and careers.
What is GDAL?
The GDAL Tools plugin offers a graphic user interface to the collection of tools in the Geospatial Data Abstraction Library http://gdal.org
These tools manage raster data by querying, reprojecting, warping, and merging various formats. They also create contour and shaded relief layers from raster DEMs, and make VRTs from raster files. You can access these tools by installing and activating the plugin.
Why dont we use spaces in file names?
Spaces in file names can cause QGIS to crash
We use underscores instead
How do we unzip a file?
unzip (extract) the files by right clicking the file and select ‘Extract All’.
How do you avoid this message?
[ “.” Files are not supported
as outputs].
This error message appears when you have not added the file type suffix. For example, you have written a field name but forgotten to add .shp for vector layers or .tif for raster layers. GIS software
is not as friendly as Microsoft Word or similar and it does not automatically add the suffix (e.g. doc). So whenever saving a file or layer please add the suffix to avoid this error message.
Why is the maps Coordinate reference system (CRS) important?
GIS uses map projections to transform the Earth’s spherical surface into a flat map. Britain uses the British National Grid, while GPS relies on the WGS84 system. In QGIS, these are called Coordinate Reference Systems (CRS). Choosing ‘use CRS from first layer added’ sets the project CRS based on the first layer added, simplifying the process and avoiding issues with mismatched CRS.
Importing Layers in QGIS
The simplest method to import layers in QGIS is to click and drag them from the browser panel to the layer panel. This avoids confusion from multiple files with the same name, presenting only one consolidated layer name in the QGIS browser. While we’ll mostly use this method, it’s important to first become familiar with the data source manager. Additionally, GIS layers consist of multiple files, highlighting the importance of proper layer management. Storing files on a memory stick ensures they’re all in one place, simplifying management and avoiding scattered storage.
The Relationship Between Objects and Attributes in GIS
In GIS, points, lines, and polygons are linked to rows in an attribute table.
This connection turns a map into a spatially organized database.
Raster images like aerial photographs lack attribute tables in QGIS, though some GIS systems include them.
Attributes provide nonspatial information about geographic features.
Attributes are stored in a table and linked to features by a unique identifier.
Example: A river’s attributes might include its name and pollution index.
Creating a Shapefile in GIS
When you create a new shapefile, you’re generating a vector layer with the extension .shp. Originally designed by ESRI, a company, shapefiles (.shp) are now universally used by GIS companies worldwide. Therefore, ‘shapefile’ and ‘ESRI shapefile’ refer to the same thing.
Using the Identify Tool in GIS
The Identify tool in GIS allows you to select which layer to retrieve data from by changing the Mode at the bottom of the window. Setting it to ‘layer selection’ takes data from the activated layer. Conversely, choosing ‘top down’ reads from the topmost active layer. You can also change how data is displayed by selecting the View option, with ‘table’ being helpful. Once activated, click anywhere to learn depth, e.g., -5m below sea level. Bathymetry, discussed in lecture, is a type of digital elevation model (DEM)
