Computer aided mapping.

Lecture index: Introduction. / Basic components of any map. / Aesthetics and conventions of map presentation. / Computer representation of map information as vector vs. raster formats. / Adobe Illustrator. / In-class map exercise. / Exercise 6.


Introduction

A primary purpose of this weeks lab is to teach both some computer mapping and air photo interpretation skills. The advantages of computers in producing maps is now so great that hand drafted maps are increasingly rare. You will also be introduced into some basic principles involved in constructing maps. These principles are very helpful in some of the subsequent exercises, especially those related to GIS.

There isn't a reading for this week, except you are urged to read through the tutorial for Inkscape (see link below), and explore the help options for this software program. It is a good idea to get used to using the internal documentation that comes with many programs. This week won't involve a lot of lecture. This is something you learn best by doing.

The most important thing to consider when constructing a map is to consider - what is the map's purpose? What information is the map to convey? What needs to be shown in order to provide meaningful context for that information? Who is your audience? The more multi-purpose a map, the more complicated and detailed it often is. Yet, such complicated maps can be hard read and understand. There is an essential tension between map simplicity providing readability, and map complexity, providing more information. A simple guide is that providing more information than is needed simply produces clutter.

Many maps are now dynamic, computer based, and they evolve as more information is collected. The beauty is that they are customizable, where the user can select that data they want. This is a key aspect to GIS, which we will consider later. This means that you might also consider what uses the map be put to in the future - how might it grow? The map becomes more than a static depiction, but is instead linked to an evolving database.

Copy of William Smith's geologic map of England and Wales, the first geologic map. Source: http://www.unh.edu/esci/WilliamSmiths-StrataIdentified/index.html .


Basic components of any map

These are basic elements that all maps need to have.


Aesthetics and conventions of map presentation.

The conventions of language help us communicate, and there are conventions associated with different types of maps that help us read them. Blue squiggly lines are easily recognized as rivers. There are conventions for geologic and geoscience maps.

Example of map legend from USGS site : http://geomaps.wr.usgs.gov/parks/gmap/gmap3.html .


Computer representation of map information as vector vs. raster formats

This is fundamental distinction that is important to recognize. Raster format is akin to a simple x,y,z image where x and y are position on the page and z is the color value of that position (or on a computer screen of that pixel). Think of the art style of pointillism where images were created with small colored dots. A raster format is attractive in its simplicity, but has some severe shortcomings. If you draw a straight line the pixel values that were there before are usually lost. More importantly once drawn it loses its identity as any sort of distinct object. The computer doesn't know which pixels belong to the line and which don't. If you want to make it longer, change its orientation or width, the original line needs to be erased pixel by pixel, then the new line drawn. Redrafting soon becomes tedious and a mess. Still some information, such as a satellite or air photo images, comes in a basic raster form.

Vector formats are where objects are defined mathematically via a suite of attributes and drawn from those. Change the objects attributes and you change its appearance without affecting anything else. These objects can be points, lines, shapes and can have all sorts of characteristics such as position, width, and color. The computer keeps track of all this information and draws the appropriate object. For geometric shapes, including polygons, this is a much more efficient and versatile way to keep track of graphic elements. Compare the amount of information it takes to specify a black square one inch on a side, with 333 dpi, in a raster versus a vector format. What is more, one information is easily retrievable for other uses in both cases. Overlapping objects can exist in vector format and so information is not lost by superimposition and the operator can decide which element should be in front of the other. A next natural step is to be able to store information about each object as hidden object attributes. You could then plot all objects with attributes in a certain range. This is a fundamental concept behind GIS. Inkscape and Adobe Illustrator can deal with both types of formats but uses vector format primarily. Adobe Photoshop is basically limited to a raster format.


Adobe Illustrator and Inkscape

Many map drafting programs exist. Autocad is probably the best known, and is in some ways the most powerful. It is geared toward engineering and architecture. Canvas is another package that has some strong adherents. Learning one of these will help somewhat with the others. Illustrator is in many ways the industry standard, as it is one of the more widely used packages. We have experience with it, and the resources are on campus. However, Illustrator is expensive, is easy to get lost in all the possibilities, and there can be problems using your files from one version to another as they bring out new versions. There is a freeware drafting program called Inkscape that we will use. If you learn how to use Inkscape, then learning Illustrator is relatively quick and easy due to the similarities. However, you can not open Inkscape files in Illustrator without a lot of effort.

Important concepts in Inkscape (and Illustrator):

Layers: One of the strengths of Illustrator is the easy ability to work in layers and then utilize whatever layers you need. These can be considered as overlays. A base map can be put in one layer, geologic features can be put in another, geographic in another, data points in another, and so on. Custom maps can then be made from the combination of layers. Elements can easily be transferred from one layer to another. We will see the importance of this layering concept in future labs. You can turn off a layer so it can't be seen, or lock a layer so it can't be modified, or set a layer so that it won't be printed. Layer management is important.

Objects: What you 'draw' in iIlustrator are a great variety of objects. These can be lines, polygons, raster images, text, graphs and combinations of the above. Objects are editable after you have created them.

Drawing lines and polygons with fill: Lines and polygons as objects have two parts to them, an outline (border) and a fill. Either one can be transparent so that you have only a border or a fill. In addition, the border can be of different line thicknesses (referred to as weights), and they can be dashed. The fills can be colors or patterns. Again, at any time you can change the character of the outline or fill. These can all be thought of as object attributes.

Handles and redrawing lines and shapes: The small ornaments along the length of the outline of an object are known as handles and can be used to reshape it. You can also use the endpoint ornaments to link to another object or to continue extending the existing line.

Multiple windows: There are multiple small windows to create and manipulate the layers and objects you create. Often, if you can't find something, it is because that window was inadvertently closed or is hidden behind another window. There are windows to choose your drawing and editing tools, a window to manage your layers, a window to choose your fills (swatches), a window to alter line or border attributes, and more.

The Help part of the software can actually be helpful.

Basic Inkscape Tutorial.


In-class map exercise.

One way to learn methods of abstraction and depiction involved in making maps is to see how others have approached this challenge. We are going to look at a very diverse suite of geoscience maps and explore some of the conventions used. You will work in groups of two. For your map complete the following:


Link to explore air photo interpretation: Natural Resources Canada - government site.


Exercise 6.


Copyright by Harmon D. Maher Jr.. This material may be used for non-profit educational purposes if proper attribution is given. Otherwise please contact Harmon D. Maher Jr.