Lecture 07 : Data Display (link to Powerpoint file)

Lab Exercise 08: Data Classification Display

GIS in Archaeology: Data Display

Basic Principles

Principles of Map Design:

1. Decide on the purpose of the map and what elements need to be included.

2. Design the map so that the most important element stands out first.

3. Choose the simplest design that serves the purpose.

4. Make map elements as readily understandable as possible.

5. Design secondary elements to complement the map purpose without distracting the reader.

Types of Maps:

General reference maps are a general purpose map designed to display elements and thier association to one another (e.g. USGS quad map). Thematic maps are designed to illustrate the distributional pattern of a specific theme. Qualitative thematic maps show the overall distribution of classes within a given theme. Quantitative thematic maps attempt to show the distribution of a specific variable for a theme: chloropleth map, dot map, graduated symbol map, chart map.

Map Output and Scale

Select and appropriate scale -- large scale vs. small scale; detail vs. overview.

Choose appropriate data and symbology for the desired output scale. You need to avoid overcrowding the map. Choose symbols and text sizes that are legible without being distracting.

Map Generalization

Generalization is a generic term to remove unnecessary detail from maps. Selection refers to eliminating unnecessary elements (e.g. restrict a US map to only contain cities larger than a certain site). Simplification is modifying complex elements downt o the simplest feature type that communicates the necessary meaning.

Map Generalization Continued

Classification Schemes:

1. Natural Breaks -- looking for naturally occuring breaks in the distribution.

2. Equal interval -- each group has the same size.

3. Quantiles -- equal number of observations in each class.

4. Standard deviation -- classes are defined on the basis of distribution from the mean. Best used for normally distributed data.

Map Presentation

Modern GIS packages provide flexible map creation through easy to use GUI interfaces. Map display overview -- map elements: map body; legend, north arrow, and scale; title, map description, and border; and inset map.

Cartographic Symbolization

Spatial Features and Symbology

Vector data can use a variety of visual cues to provide map information: symbol types, symbol colors, symbol size and texture, and symbol shape and pattern. Raster data generally use on ly color schemes to provide map information. In some circumstances it is useful to convert these to vector data types (e.g. contour maps for digital elevation data). Transparency can be a useful tool for combining multiple raster data sets in a single output.

Cartographic Symbolization (continued)

Vector Data Symbology:

Map symbols -- you generally use symbols that match the feature type of the coverage (e.g. point symbols for point features, line symbols for line features). However, sometimes it is useful to violate this rule.

Cartographic Symbolization (continued)

Vector data visual variables

1. Color: hue -- dominant wavelenght of the color (red, green, blue, etc.), value -- lightness or darkness of the color, and chroma -- saturation of the color (fully saturated is the true color, low saturation tends to gray)

2. Size

3. Shape and pattern

Mapping Schemes for Vector Data

Quantitative Data: symbol size and color value

Qualitative Data: color hue, symbol shape, symbol pattern

Color Mapping Schemes for Quantitative Data

1. Single hue scheme -- uses a single color but varies from lighter to darker.

2. Hue and value scheme -- progresses from light vale of one hue to a dark value of another hue.

3. Diverging/double-ended scheme -- graduated color between two dominant colors. This is a good choice when you want to display data that are above or below some mean point.

Typography

Typographic variation assists in map understanding.

1. Typeface -- the main character type or font of the type.

2. Type size

3. Type form: weight, width, upright vs. slanted, case (lower, upper, mixed)

4. Type color: color, shadowed, fill

Typographic Placement Techniques

Typographic Placement

It is recommended that you place text to the upper right of a point symbol. It is recommended that you place text parallel to or following the course of line symbols. It is recommended that you place text inside polygon features. However, there are virtually always reasons to make exceptions to these general rules.

Typographic Variation Techniques

Typographic schemes: Qualitative data -- best to vary by typeface, color, style; Quantitative data -- best to vary by size, weight, and/or case. Typographic legibility: you need to take into account the final output size and format whenmaking decisions on typographic sizes and styles. It is often good to use different types for different map elements.

Map Design

Well designed maps easily communicate information; poorly designed maps obscure important map information. The layout and focus of the map should draw the reader to the important element(s) of the map design. The optical center of a map is just above the center of the geometric center.

Map Design Layout (continued)

Other map elements should be designed to draw the reader's attention in proportion to their importance. You want the overall map to look well distributed rather than being heavily weighted to certain areas and sparse in others.