The Programming Historian (Dec 2013)
Creating New Vector Layers in QGIS 2.0
Abstract
In this lesson you will learn how to create vector layers based on scanned historical maps. In Intro to Google Maps and Google Earth you used vector layers and created attributes in Google Earth. We will be doing the same thing in this lesson, albeit at a more advanced level, using QGIS software. Vector layers are, along with raster layers, one of the two basic types of data structures that store data. Vector layers use the three basic GIS features – lines, points, and polygons – to represent real-world features in digital format. Points can be used to represent specific locations, such as towns, buildings, events, etc. (the scale of your map will determine what you represent as a point – in a map of a province, a town would be a point, whereas in a map of a town, a building might be a point). Lines can effectively represent features such as roads, canals, railways, and so on. Polygons (effectively enclosed shapes with more than a few sides) are used to represent more complex objects such as the boundaries of a lake, country, or electoral riding (again, scale will affect your choice – large buildings in a close-up map of a city might be better represented as polygons than as points). In this lesson you will be creating shapefiles (which are a type of vector data) to represent the historical development of communities and roads in Prince Edward Island. Each shapefile can be created as one of the three types of features: line, point, polygon (though these features can’t be mixed within a shapefile) . Each feature you create in a shapefile has a corresponding set of attributes, which are stored in an attribute table. You will create features and learn how to modify them, which involves not only the visual creation of the three types of features, but also the modification of their attributes. To do so, we will use the files from Installing QGIS 2.0 and Adding Layers concerning Prince Edward Island.
