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GTECH 361

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

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GTECH 361

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

  2. Today’s Content • Techniques for choosing and modifying symbols and text

  3. 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

  4. Two Map Categories • Reference Maps • Multi purpose • Thematic Maps

  5. Effective Symbolization • Pictorial symbolsa picture says more than a 1,000 words

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

  7. 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.,

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

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

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

  11. Representing Categories

  12. Representing Quantities

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

  14. Classification Methods • Natural breaks • Quantile • Manual • Equal interval

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

  16. How to Decide, part II

  17. 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

  18. 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

  19. 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

  20. Mapping Proportion

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

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