Lecture 02 The Basics pf Creating a GIS Map GTECH 361 Lecture 02 The Basics pf Creating a GIS Map

Today’s Content Techniques for choosing and modifying symbols and text

Today’s Objectives choose symbols for point, line, and polygon features modify symbol properties such as color, size, and outline label map features using an attribute and by adding text symbolize features to show type, rank, or amount group features into classes and apply symbols to each class compare different methods of grouping features into classes correct visual distortion caused by differences in area show proportional amounts on a map by normalizing data symbolize features to show density

Two Map Categories Reference Maps Multi purpose Thematic Maps

Effective Symbolization Pictorial symbols a picture says more than a 1,000 words

Types of Symbols Point Line Polygon Marker Symbol Color Size Angle Line symbol Polygon Fill color Fill pattern Outline color Size Angle Width Outline width Background color

Symbol Sets ArcGIS comes with 25 off the shelf You can create or import your own Similar symbols in vastly different symbol sets, e.g.,

Labeling (Map) Features Retrieving label value from field value in the feature’s attribute data

Label vs. Annotation Manually adding a label describing a map feature that has representation in the underlying dataset Dynamic labels are context-dependent

Representing Attribute Values All features of a layer are the same Differentiation according to feature’s attribute value

Representing Categories

Representing Quantities

Classifying Data Three decision prior to classification How many classes? What method to use for placing the values into classes? What kind of symbology?

Classification Methods Natural breaks Equal interval Quantile Manual

How to Decide (on a classification scheme) Rule of thumb: 3 - 7 classes Classification histogram

Classification method How many classes to have How to Decide, part II Classification method When to use How many classes to have Natural breaks When attributes are distributed unevenly across the overall range of values Look for natural groups Equal interval When you want all classes to have the same range Easily understood interval, such as 2, 50, 1000, etc. Quantile When attributes are distributed in a linear fashion Determined by purpose of the map Manual When you want classes to break at specific values

Proportional Symbology Absolute quantities can be misleading When quantities vary a lot When size of geographic feature varies a lot Solutions Mapping density Mapping proportion

Normalization Divide value of an attribute by value of another attribute Most commonly by area resulting in density Already normalized data should not be normalized by yet another attribute

Dot Density Maps Each dot represents a specific amount Dots map randomly within each polygon Individual dots in a dot density map are not associated with actual location coordinates

Common reasons to map attribute relationships Mapping Proportion Common reasons to map attribute relationships What to map Example Proportion of the part to the whole Countries: Bushels of wheat exported normalized by bushels of wheat harvested Rate of something Counties: Cases of heart disease normalized by total population Relationship of one characteristic to another Schools: Number of students normalized by the number of teachers Relationship of one time period to another Sales territories: Last year's sales revenue normalized by this year's sales revenue

Representing Proportions Ratios between 0 and 1 Percentages (ratios multiplied by 100) Rates based on a round number Per person Per 100 Per 1,000