Brief Summary
This workshop provides an introduction to GIS (Geographic Information Systems), covering definitions, applications, data types, software options, coordinate systems, and initial steps for new users. It emphasises the versatility of GIS across various disciplines and offers resources for further learning.
- GIS is a computer-based tool for storing, visualising, analysing, and interpreting geographic data.
- GIS can be used to view, create, and analyse spatial data, answering questions about location, patterns, trends, and impacts.
- Vector and raster data are the two primary types of spatial data used in GIS.
- Various software options are available, including commercial (Esri), open source (QGIS), and free tools (Google Earth Pro).
- Understanding projections and coordinate systems is crucial for accurate spatial analysis.
Definitions
GIS, or Geographic Information Systems, are computer-based tools used to store, visualise, analyse, and interpret geographic data. The main functions of GIS involve creating geographic data, managing it in a database, analysing it to find patterns, and displaying it on a map. Geographic information includes place names (political units, natural features), administrative units (zip codes, census tracts, school districts), street addresses, and coordinates (latitude, longitude, UTM).
What is GIS used for?
GIS can determine the features present in a specific location and identify the locations of particular features. It helps analyse the distribution of elements on a landscape, identifying patterns such as even distribution, random scattering, or clustering, and explore factors influencing these patterns across various fields like natural sciences, social sciences, and medicine. GIS is used to study how the presence or distribution of a feature changes over time by examining maps from different periods and to evaluate the impacts of changes, determining how changes in one element affect others on the map. Furthermore, GIS aids in forecasting, predicting how changes might occur and to what extent, as seen in climate models predicting shoreline changes with temperature increases.
Types of data used in a GIS
GIS uses two main types of data: spatial and tabular. Spatial data represents what is seen on a map, while tabular data is associated with vector data and provides additional information. Vector data consists of points, lines, and polygons, created by positioning a mouse cursor and clicking to create features. Raster data, like images, uses an array of squares (pixels) with assigned values, providing more localised information than vector data.
Vector data
Vector data involves points, lines, and polygons, similar to drawing on paper. Points are created by clicking a mouse, while lines and polygons require clicking to create vertices (pivot points) for changes in direction. The choice of using points, lines, or polygons depends on the map scale; points may suffice for cities on a continental map, but polygons are needed when zoomed in. The most common vector data file format is a shapefile, which includes both geometry and attributes. Shapefiles come in zip files containing multiple files, all of which are needed to create the layer in a GIS.
Raster data
Raster data is similar to images, consisting of an array of equally sized squares (pixels), each with an assigned value. A raster digital elevation model (DEM) shows elevation through pixel values, providing detailed variability information. Image classification can be performed on raster data to categorise the image based on pixel values, such as classifying areas as water, man-made features, or natural land cover. Spatial data can be created by mapping points, lines, and polygons, or acquired through drones with cameras or sensors. Existing files of vector or raster data can be found in data repositories or portals maintained by government agencies, non-profit institutions, universities, and companies like Esri.
Tabular data
Tabular data, associated with vector data, is stored in an attribute table within the GIS, containing characteristics of map features. Each row corresponds to a feature on the map, and each column contains a different type of information, such as textual data, numbers, or links. An ID number links each record in the table to a feature on the map, allowing for the display and analysis of data in various combinations. Tabular data can be populated while mapping, collected in the field via apps, or obtained from existing sources like shapefiles, CSV files, Excel tables, or GPS databases. The table must have a field with coordinates or a geographic identifier (place name, address) to link records to mapped features.
GIS software options
GIS software options include commercial software (e.g., Esri's ArcGIS), open-source software (e.g., QGIS), and other tools like Google Earth Pro. Esri is a market leader with products like ArcGIS Pro (desktop application for Windows, requires significant memory) and ArcGIS Online (cloud-based, accessible on any computer). Other companies like Carto offer GIS software, while QGIS is a free, open-source option compatible with Mac and Windows. GRASS GIS, often bundled with QGIS, is known for its raster data capabilities. Google Earth Pro is a free desktop application with unique features and limitations, and Google Earth for web is a more lightweight online version.
Projections and coordinate systems
Projections are methods to translate the Earth's three-dimensional surface onto a two-dimensional map, with common types including cylindrical, conical, and planar projections. In any projection, some attributes (shape, area, distance, direction) must be distorted, so the choice depends on the map's purpose. Coordinate systems, such as latitude and longitude, are used to specify locations on the Earth's surface, with hundreds of systems available. A datum is a point on the Earth's surface that links the model used to create the projection to the actual Earth's surface.
Typical first steps in using a GIS
Typical first steps in using a GIS include choosing a base map (imagery, streets, topography) to provide a background for the data. The order of layers in the layers list affects visibility, with layers higher in the list potentially covering those below. The symbology of points, lines, and polygons can be changed (colour, size, effects) to improve visualisation. Selection tools allow users to filter and edit features, assess attributes, and perform queries based on specific attributes. Users can create features or perform analysis using built-in tools, often without needing to write code.
Resources
Various resources are available for learning more about GIS, including online videos and suggested websites. The UCR Library offers workshops on various topics, and contact information is provided for questions about GIS resources and assistance at UCR.
