Displaying Data ENVS 521 Lecture 4

Objectives Layer properties Symbolize data Label features Definition queries http://www.esri.com/mapmuseum/mapbook_gallery/volume25/pdf/mapbook25_35.pdf

Layer Properties All aspects of a layer are controlled through the layer's properties. Some of the properties you can define include: How to draw the layer What data source the layer is based on Whether to label the layer Attribute field properties The Layer Properties dialog box will be different for different types of geographic data. ArcGIS Desktop Help

Symbolizing vector data in the layer properties Right click on the layer in the TOC  Properties  Symbology Tab

Symbolize Data by Clicking on Symbol in TOC Click once on the layer symbol in the TOC to bring up the symbol palette: Click once on the symbol with your mouse to bring up the symbol selector

Symbolizing using a single symbol for all features

Symbolizing Categories: Unique Values Select the value from the attribute table to symbolize on. Add all values – will add all attribute values Add Values – will add selected values end user inputs that are found in the attribute table. Set symbology Don’t forget to click Add All Values

Symbolizing Categories: Unique Values Many Fields Select the value fields to symbolize on (this is an attribute field) Click Add All Values ArcMap will symbolize on the unique combination of the fields selected. Set symbology: Color ramp Group values Work with individual or a select group of symbols

Symbolizing Quantities ArcMap uses attribute information and a classification scheme to set symbology. Select colors, symbols, proportional symbols or dot density. Set value field. Set normalization if appropriate. Select classification scheme. Set the number of classes.

Using Normalization

Quantity Classifications

The histogram X-axis shows the range of values in the field. Y-axis is a count of features. Vertical blue lines are class breaks (also shown in the Break Values box). A single gray column represents a percentage of the value range. The default number of gray colums is 100 hundred. The lowest value is 10 and the highest is 89. The value range is therefore 79, of which 1% is represented by a single gray column (which is 0079). The first gray column has a value of 1. That means 1 feature has a value of 10. Each gray column is 10 + 1% of 79 + 1% of 79…because each gray column represents 1% increment increase in value.

Manual Classification End user selects number of classes End user sets class break values Click OK Set symbology

Equal Interval Divides the range of attribute values into equal-sized subranges. End user specifies intervals and ArcMap determines where the breaks should be. INSTAR values range from 10 to 90 (range = 80). Set equal interval for 5 classes. 80 / 5 = 16. Best used for familiar data (precipitation or temperature). ArcGIS Desktop Help

Defined Interval End user specifies the interval to equally divide a range of attribute values. Rather than specifying the number of intervals you specify the interval value. ArcMap automatically determines the number of classes based on the interval. Click OK. Set symbology. ArcGIS Desktop Help

Quantiles Each class contains an equal number of features. This method classifies data into a certain number of categories with an equal number of units in each category. For example – INSTAR has 1194 points. User defines 5 classes or breaks Each class will have approximately 238 observations. Some observations cannot be evenly split between categories so this is just an approximate number, so classes may have 246 or 277 or 238. A quantile classification is well suited to linearly distributed data. Be careful as features are grouped by numbers, so similar values may be grouped into adjacent classes because of the quantile it falls within. Because features are grouped by the number in each class, the resulting map can 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. ArcGIS Desktop Help

Natural Breaks Classes are based on natural groupings inherent in the data. ArcMap identifies break points by picking the class breaks that best group similar values and maximize the differences between classes. The features are divided into classes whose boundaries are set where there are relatively big jumps in the data values. A method of statistical data classification that partitions data into classes using an algorithm that calculates groupings of data values based on the data distribution. Jenks' optimization seeks to reduce variance within groups and maximize variance between groups. Natural Breaks Step 1: The user selects the attribute, x, to be classified and specifies the number of classes required, k Step 2: A set of k‑1 random or uniform values are generated in the range [min{x},max{x}]. These are used as initial class boundaries Step 3: The mean values for each initial class are computed and the sum of squared deviations of class members from the mean values is computed. The total sum of squared deviations (TSSD) is recorded Step 4: Individual values in each class are then systematically assigned to adjacent classes by adjusting the class boundaries to see if the TSSD can be reduced. This is an iterative process, which ends when improvement in TSSD falls below a threshold level, i.e. when the within class variance is as small as possible and between class variance is as large as possible. True optimisation is not assured. The entire process can be optionally repeated from Step 1 or 2 and TSSD values compared From http://www.spatialanalysisonline.com/output/html/Univariateclassificationschemes.html ArcGIS Desktop Help

Geometrical Interval Class breaks are based on class intervals that have a geometrical series. A geometric series is a pattern where a constant coefficient multiplies each value in the series. The geometric coefficient in this classifier can change once (to its inverse) to optimize the class ranges. The algorithm creates these geometrical intervals by minimizing the square sum of element per class. This ensures that each class range has approximately the same number of values with each class and that the change between intervals is fairly consistent. Used for visualizing continuous data and to provide an alternative to the Natural Breaks (Jenks), quantiles, and really any variance minimized (within classes) classification method. Specific benefit is that it works well on data that are not distributed normally, works well on logarithmic distribution. This method was designed to work on data that are heavily skewed by a preponderance of duplicate values, e.g., 35% of the features have a value of 2.0. The table below is an example of a geometrical interval classification that was produced in ArcMap. The interval (or bin size) of the class is calculated by subtracting the minimum from the maximum. The geometric coefficient is calculated by dividing the previous interval by the current interval. ArcGIS Desktop Help https://blogs.esri.com/esri/arcgis/2007/10/18/about-the-geometrical-interval-classification-method/

Standard Deviation Classification scheme shows how much a feature's attribute value varies from the mean. ArcMap calculates the mean values and the standard deviations from the mean. Class breaks are then created using these values. ArcGIS Desktop Help

Charts Uses attribute data to create charts as symbols Used to present large amounts of quantitative data in an eye-catching fashion ArcGIS Desktop Help

Multiple Attributes Multi-variate maps using two attributes to symbolize on. An example could be land use and habitat degradation or watershed and impervious surfaces.

Symbolizing Rasters You can symbolize rasters by: Grouping their values into a number of classes Stretching the values to enhance contrast Assigning each unique value in the raster to a color Symbolize based on the raster type (continuous or discrete)

Displaying Rasters

Symbolizing Rasters as Classified Single band rasters (i.e. elevation, slope) can classified using the same classes as learned for vector classification – groups cells into categories: Click on the classified and let ArcGIS build any histograms it needs to display the classifications. ArcGIS Desktop Help

Symbolizing Rasters as Stretched Displays continuous raster cell values across a gradual ramp of colors. Use the Stretched renderer when you want to draw a single band of continuous data. images may not contain the entire range of values your computer can display; therefore, you could stretch the image's values to utilize this range by applying a contrast stretch. This may result in a crisper image, and some features may become easier to distinguish. ArcGIS Desktop Help

Discrete Data

Symbolizing Data with RGB Composite Aerial photo’s or satellite imagery 3 or multi-band raster layer

I did all this work to symbolize my data, how can I store the symbology and associate it with a particular shapefile?

Layer Files A layer file is a file that stores the symbology. This file can exist outside of the map you’ve built. Layer file can be used on the file it was created or applied to other shapefiles or feature classes if the data layers have the same geometry and schema (or attribute) upon which the symbology was created. A layer file ends in the extension “.lyr” Stored on the network as 1 file. Layer files read the data source according to the network path – if you move a layer file, you may need to reset the data source. Think CARTOGRAPHY when you think of a layer file. A layer file is NOT a data layer, it’s simply a file that stores information about the symbology of the original data layer.

To create a layer file, set the symbology – right click on the layer in the TOC – save as a layer file. Navigate to where you want to save the file. Hit save.

Layer file is added to TOC, data are read from the original data layer the layer file was created from. If the link is broken, a red ! will appear and you will have to reset the data source. To reset the data source, go to the layer properties, under the source tab navigate to the original dataset.

Importing symbology from a layer file To apply a layer file… right click on the layer – properties – symbology Click import and navigate to where the layer file is saved, hit ok. The matching dialog box will appear. Map the attribute field in the layer in the TOC that corresponds to the attribute used in the layer file from which symbology was generated. These fields can have different names, but the field type and data contained in the attribute field should be the same (data should be in the same range and must be the same type). Hit ok.

Layer Packages Consists of the layer and the dataset the layer file references. Lets you share the data, symbology, labels, and table properties. Is a larger file size than layer files because it includes the data. File extension is .lpk. Add the .lpk to ArcMap, data will display. Note the source tab to see where the data the layer files reference is stored.

Creating a layer package Be sure each layer has a description filled out (right click on layer  properties  General tab). Right click on layer  Create Layer Package Follow wizard. Click validate. Address issues. Validate until no issues found. Click Share.

Layer Properties: General

Layer Properties: Source

Layer Properties: Selection

Layer Properties: Display

Layer Properties: Symbology

Layer Properties: Fields

Layer Properties: Definition Query

Syntax ArcGIS use Structured Query Language (SQL) and Boolean Language to build structured query requests. Boolean language: AND OR >, <, =, >=, <=, not, = Uses attribute information to execute the query.

Use of OR If the attribute field that holds county name is County_Name, query would look like: County_Name = ‘Albemarle’ or County_Name = ‘Accomack’ If interested in area or a number, don’t use quotes Area > 75000

Use of AND If an attribute table has a field called CountyName, would ArcGIS be able to execute this query: County_Name = ‘Albemarle’ and County_Name = ‘Accomack’ ??

Use of NOT Use at the beginning of the expression: NOT County_Name = ‘Albemarle Shows where have county names that are not Accomack

Layer Properties: Labels Turn labels on by right clicking on layer and clicking labels or by checking Label features in this layer in this dialog box.

Label Styles

Text Properties

Placement Properties

Label Priority and Weight Ranking

Adding Labels with the New Text Tool Label of the top most layer in TOC that is turned on will be labeled Label will be the primary display field (check properties  fields)