 ftp://edacftp.unm.edu/outgoing/pub/spenman/geog581L/exam ples_visualization EDAC FTP SITE

SHAWN L. PENMAN EARTH DATA ANALYSIS CENTER UNIVERSITY OF NEW MEXICO DATA VISUALIZATION

 When Maps Lie (CityLab)  Posted on UNMLearn ADDITIONAL READING

 Your personal style is the default location for new symbols and style elements to be saved to. It is empty to begin with but can be used to organize your style contents. It will always be referenced by ArcMap.  On Windows XP, it is located at :\Documents and Settings\ \Application Data\ESRI\Desktop10.0\ArcMap.  On Windows Vista and Windows 7, it is located at :\Users\ \AppData\Roaming\ESRI\Desktop10.0\ArcMap. STYLE LOCATION

CLASSIFYING FEATURES

QUALITATIVE VS QUANTITATIVE  Qualitative  Data classified or shown by category, rather than amount or rank  eg. soil by type  animals by species  Different types of disasters  Quantitative  Data grouped or shown by measurements of number or amount  eg. population per unit area  percentages  amount of damage caused by disaster

Equal intervalNatural breaks QuantileStandard deviation CLASSIFYING QUANTITATIVE VALUES

CLASSIFICATION TOOL

 Automatic or default settings by software are almost never appropriate  Different classification can create a very different “look” of your data – you want control over this  Certain classifications for certain data sets can be plain wrong, or very misleading at best  Proper classification techniques assist in making the “map speak for itself” WHY CLASSIFY DATA?

Natural breaks Quantile Equal interval Standard deviation

 Equal interval divides the range of attribute values into equal- sized subranges. This allows you to specify the number of intervals, and ArcGIS will automatically determine the class breaks based on the value range. For example, if you specify three classes for a field whose values range from 0 to 300, ArcGIS will create three classes with ranges of 0–100, 101– 200, and 201–300.  Equal interval is best applied to familiar data ranges, such as percentages and temperature. This method emphasizes the amount of an attribute value relative to other values. For example, it will show that a store is part of the group of stores that make up the top one-third of all sales. EQUAL INTERVAL

 Natural Breaks classes are based on natural groupings inherent in the data. Class breaks are identified that best group similar values and that maximize the differences between classes. The features are divided into classes whose boundaries are set where there are relatively big differences in the data values.  Natural breaks are data-specific classifications and not useful for comparing multiple maps built from different underlying information. NATURAL BREAKS

 Each class contains an equal number of features. A quantile classification is well suited to linearly distributed data. Quantile assigns the same number of data values to each class. There are no empty classes or classes with too few or too many values.  Because features are grouped in equal numbers in each class using Quantile classification, the resulting map can often be misleading. Similar features can be placed in adjacent classes, or features with widely different values can be put in the same class. You can minimize this distortion by increasing the number of classes. QUANTILE

 The Standard deviation classification method shows you how much a feature's attribute value varies from the mean. ArcMap calculates the mean and standard deviation. Class breaks are created with equal value ranges that are a proportion of the standard deviation—usually at intervals of 1, ½, ⅓, or ¼ standard deviations using mean values and the standard deviations from the mean. A two-color ramp helps emphasize values above the mean (shown in blue) and values below the mean (shown in red). STANDARD DEVIATION

Standard deviation of daily mean ( ) precipitation (units: mm day -1 ) in the URD for JFM, AMJ, JAS and OND.

 Understand what your data represents  are there any categories or values of importance?  what underlying distribution could you expect?  Study the distribution  e.g. use the histogram in the classification tool  Try out a couple of different approaches  this is very quick….  Always consider a manual classification as an option  Identify outliers and select how to deal with them:  place them into a separate class  group them with the next closest class  create a special symbol for them CHOOSING A CLASSIFICATION

DATA SPECIFIC CLASSIFICATION EPA Arsenic Levels Arsenic-rich ground strata are common in many parts of New Mexico and ground water arsenic is routinely found in the range of ug/L. USEPA Arsenic drinking water standard is 10 micrograms per liter.

HOW MANY CLASSES?

 Maximum = 7  most map readers can distinguish up to 7 different colors on a color ramp or gray scale, so more than 7 classes will make it difficult to identify features in the same class  more than 7 classes can be used for continuous data (e.g. elevation, temperature)  Minimum = 3  fewer than 3 classes will not show much variation  Strategy  first determine the proper classification scheme  than start with large number of classes  reduce number stepwise and select the minimum number of classes which still shows the spatial pattern in sufficient detail DECIDING HOW MANY CLASSES

 The values of the class should be meaningful  % is too detailed  73.9 or 74 % is probably OK  70% may not be detailed enough  You can use standard classification schemes but typically it is better to force rounding to a certain number of digits.  For example:         MAKING CLASSES EASIER TO READ

 Select classification method  Set number of classes  Use Exclusion tool for missing or incorrect data  Manually move, add or delete breaks  Right-click the histogram to:  Zoom in/out  Insert/Delete breaks  Center the histogram USING THE CLASSIFICATION HISTOGRAM

 00s s DON’T FORGET ABOUT ARCMAP HELP (DESKTOP OR ON-LINE)

LABELING FEATURES

 Label all features dynamically using attribute values LABELING FEATURES - DYNAMIC

LABEL PROPERTIES CONTROL APPEARANCE AND POSITION

LABEL STYLES

LABEL MANAGEMENT Labeling Toolbar

LABEL MANAGEMENT Labeling Toolbar Maplex Labeling Engine – better way to label

MAPLEX

PLACEMENT PROPERTIES

LABELING FEATURES – INTERACTIVE (OR ONE AT A TIME)

 Essential labeling concepts  t t  Maplex help  ARCGIS HELP LABELING

 ftp://edacftp.unm.edu/outgoing/pub/spenman/geog581L/exam ples_visualization EDAC FTP SITE

 USA Counties  Graduated colors – Asian  Normalization – sqmi  NM Gross Receipts  Classify on Rates - look at histogram, notice how intervals change when different methods selected  Equal interval  Natural Breaks  Quantile  Standard Deviation  Label the political unit (use Name attribute field)  Use standard label engine  Use Maplex label engine – what is the difference? DEMO/PRACTICE

 South American Earthquakes  Graduated symbol map of Magnitude  Only show records 3-6  Option 1 – Exclusion of unwanted data DEMO/PRACTICE

 South American Earthquakes  Graduated symbol map of Magnitude  Only show records 3-6  Option #2 – Definition Query DEMO/PRACTICE Write Query Query Fewer Records

 School District Boundaries  Schools  Label School Districts  Label Schools – Change Scale Range so school labels only show up at appropriate scale. DEMO/PRACTICE