Introduction to GIS

SGO1910

Introduction to GIS

Spring 2004

Map basics

A map's function is to communicate geographic information. Carefully arranging the components displayed on the map results in an effective map and one that is more economical to produce.

Maps can be simple or very complex. Their purpose is to deliver the necessary information in the simplest and most complete way possible.

The designer can arrange the various map objects, also called components or elements, in limitless ways. A key initial step in designing a map is preparing a graphic outline. The designer uses cartographic principles, including visual balance and visual contrast, when creating this graphic outline. The goal is to create distinct visual "levels" to assist the reader in comprehending the map.

A map displays geographic features contained in your database. Multiple datasets or portions of datasets can be displayed in a single map. In the example below, the map features are used in the map body and also in other components of the map.

In this example, geographic features are used in the map body, the detail insets, as well as in the "inset" that looks like two globes to help the reader locate the features in the map body.

The map body is the main focus of the map and should be prominently displayed. All other map elements should support the map body and not redirect attention away from it.

Using the proper symbology, combined with feature selection based on attributes, will best illustrate the features and the "story" you want to tell with your map.

When you are symbolizing qualitative feature attributes, be sure to vary the pattern, texture, and color of the symbols. When features represent different objects or traits, make them look obviously different.

When you are displaying quantitative feature attributes, vary symbol color, value, and size. Because this type of data represents different values for the same attributes, the symbols should look as though there is a natural grouping to the features.

The map body does not have to be in any one data format. You could use a coverage, grid, TIN surface, scanned image or photo, AutoCAD drawing, data on the Geography Network, and so forth.

Marginalia

Marginalia refers to any of the supporting objects, or elements, on a map that help the reader interpret the map.

Without the marginalia, the reader has much less information about map's subject. In this example, the insets actually contain the detailed population information about the map body features.

Title
The map title should appear larger than the source or legend text but should never overpower the map body. Its placement does not have to be at the top center of the map, but it should always be easy to see and reflect the map's purpose.

Legend
The legend should be large enough for the reader to interpret the symbology. The symbols used in the legend should exactly reflect the symbols used in the map body. The legend should never be scaled independently from the map body. The legend should also be self-explanatory. The purpose of the legend is to help the reader interpret the map body. If the legend needs any type of interpretation, then it has failed its purpose.

North arrow
A north arrow can be represented in a variety of ways, but you should avoid using north arrows that are overly intricate and difficult to read. They should not be so large that they divert attention from the map body.

Scale bar
Scale bars are frequently located at the bottom of the map to make them easy to find. Remember, map scale can be represented as a verbal scale (1cm = 1 km) or as a representative fraction (1:24000 or 1/24000).

Borders and neatlines
Borders accent and define a frame. In the example above, they are used around the map body and several of the insets. Neatlines can be used to highlight or define a group of map elements. In the example above, a neatline encloses all the map elements and defines the edges of the map. Generally, neatlines and borders should not be too bold or use symbols that distract the reader.

Source information and other text
Source information provides the reader with additional information, such as the map author, organization, production date, data source date, projection, coordinate system, and how the map was produced.

Inset maps
Inset maps provide location information about the map (the map area's location in the world) or a larger-scale view of a selected map region.

Types of maps

It is a difficult task to try to classify maps, but they can be divided into two basic categories: general and thematic.

General maps show locational or positional data. They depict a variety of features and are generally useful to multiple disciplines. That is why they are called "general." Examples of such maps are atlas maps and topographic maps produced by the United States Geological Survey or Statens Kartverk.

This is a close-up of a USGS 7.5" quadrangle, which shows a variety of features.

Thematic maps show the structure and distribution of phenomena. A population map of a country is an example of a thematic map. Thematic maps generally depict a single attribute or relationship, but it is not unusual for more complicated thematic maps to show several map feature attributes or relationships. Thematic maps fall into two categories: qualitative and quantitative.

Qualitative thematic maps depict different features with different symbols according to some attribute. For example, on a map of soil types, each soil type would be represented with a different colored or patterned symbol. Areas on the map would be displayed with the symbol of the soil type found on the land. The example below displays governmental administrative regions using different symbols.

This map shows regions in Wisconsin. Each region is represented with a differently patterned symbol.

Symbology is important for showing qualitative differences among map features. You can vary the color, shape, texture, orientation, and placement of symbols to differentiate features and create a pleasing map.

Quantitative thematic maps show differences in features' numeric attributes. One way to show quantitative differences among features, such as different population densities or soil pH values, is by classifying the data, or grouping it according to numeric values. You can use different color shade values (lighter to darker shades of one color, for example) or different symbol sizes (larger to smaller circles or squares) to show a range of values.

When you classify features, all features falling into the same class are symbolized with the same shade or same-size symbol. The example below uses a color ramp to display population density for each county.

This thematic map shows Wisconsin counties grouped according to population density.

Making maps in ArcMap

So far in this course, you have been displaying and querying spatial data using ArcMap's Data View. Data View is the all-purpose viewing option for exploring, displaying, querying, editing, and analyzing data. Data View allows you to focus on the data, but it doesn't allow you to add cartographic elements such as north arrows and scale bars.

To add map elements such as titles, legends, and scale bars to your display you need to work in ArcMap's' Layout View. The Layout View lets you produce cartographic quality digital and hardcopy maps using the information contained in your data frames, reports, and graphs.

Layout View

Layout View is the ArcMap viewing option used to prepare maps for presentation and reports. In Layout View, you work with a virtual page upon which you place and arrange map elements including titles, north arrows, scale bars, legends, and the map body. In Layout View, you can do almost everything you can do in Data View, but you can also design your map.

When you work in Layout View, you can add map elements such as a north arrow, scale bar, neatline, and legend. If your Table of Contents has more than one data frame, you can use one of them to create a location (inset) map.

When you switch from Data View to Layout View, the Layout toolbar becomes active. The Layout toolbar has its own Zoom In and Zoom Out buttons, as well as a box that displays the percent reduction or enlargement (shown below with 100%).

When you zoom in or out on the map in Layout View, the amount of detail you can see on the map changes but the map scale does not.

Do not confuse the Layout toolbar's Zoom In and Zoom Out buttons with the zoom buttons on the Tools toolbar. The buttons on the Layout toolbar allow you to zoom in and out so you can see how the map elements will look at different percent reductions and enlargements. Your computer monitor's screen cannot show the full size of the map (e.g., a 36 in. x 24 in. map) so these buttons allow you to look at a "real size" map (i.e., at 100% enlargement). In this way, you have more control over your map design because you know exactly how your symbology and elements will look at their actual size.

As you zoom in or zoom out at different percentages using the Layout toolbar, notice that the actual scale of the map (either inherited from the scale set in Data View or as set in Layout View) remains the same (shown above at 1:10,000).

Adding map elements

Maps can contain more than geographic data. In your map design, the geographic data may be used to locate the subject matter and to display the spatial relationship of various features, but the overall composition of the page is held together by the discrete use of graphic devices such as:

• Map title
• Graphic elements like borders
• Photographs, logos, and illustrations
• Graphs
• Reports

These devices help guide the viewer across the map page, focus attention by emphasizing specific components, and organize items that relate to one another or belong together. In a map series, map elements like logos and consistent borders can help tie the series together and promote a professional appearance.

Use graphic devices such as borders, graphs, and logos to help organize a map layout and create consistency for a map series.

A good title puts the map in perspective. Most maps have titles and you may want to consider the use of subtitles if you are planning to create a map series. Develop the working titles for your maps either before or during the design phase. Use the working titles as placeholders in your composition. You can always edit them before you finalize your maps.

Graphic elements such as lines and boxes ornament the map but also organize and call attention to various aspects of it. The color and weight of lines should work to group related parts of the map together or emphasize one part over another. In ArcMap, you can create a border for any graphic element by right-clicking it, then choosing Properties and clicking the Frame tab.

Images of people, places, or objects that exist in the map area can provide an essential visual link between the actual subject matter and the abstract quality of the map. Images can include digital photographs, scanned materials, logos, and graphics created with other programs.

Graphs and reports summarize complex tabular information. Once you've created a graph or report, you can place it on your map to make your map more influential or instructive.