The Scenario After your presentation of the school age students in the county based on the results of your map created in the previous exercise, the county would like to see all of the major schools also displayed. Exercise 6: Symbolizing your data Colors and patterns can be an amazing thing. The rich colors or blue, orange and red in a sunset, the hot pink and day-glow green found in 80 s fashion, or even the use of a striped shirt with a plaid skirt. The use and misuse of colors can say a lot about the message you are trying to convey. The same is true in Cartography, or map making. Cartography is a neat mix of artistic talent and scientific precision. The best quality maps consider both of these elements, presenting the most important data in a visually appealing way. In this exercise you will work with several different types of data and use many of the symbology tools to present the data in an informative and elegant manner. And for those still wearing day-glo 80 s fashion, your instructor might request that you print in black and white. In this exercise you will: Prepare data for your mapping project Extract data based on the spatial extent of another layer Symbolize your data using a variety of tools
Exercise 6: Symbolizing your data Selecting features based on location Before you begin, you will need to create a new ArcMap document and add the following data. State wide schools: see Appendix B: Data sources Road and other line features: see Appendix B: Data sources County wide census blocks: Developed in exercise 6. State wide counties: see Appendix B: Data sources In this task, you will select the schools that fall within your county and export the selected features as a new layer. 1. On the main menu, click Selection and choose Select by Location. This will open the Select by Location dialog box. 2. In the I want to... field, leave the default value of Select features from option. 3. In the layers window, click the check box next to CA_ Public_Schools. 4. In the That... field, use the drop down menu to select are completely within. 5. In the the features in the layer field, select the county wide census data layer. 6. Click OK to select the school features that are completely within county and close the Select by location dialog box. 7. Now, Export the selected features as a new layer as outlined in the previous exercise and add the new shapefile to the map document. 8. Remove the statewide school layer from your map document. 2 3 4 5 6 Page 2
Exercise 6: Symbolizing your data Symbolizing based on categories 3 This is the same process that you did in Exercise 2 when symbolizing specific roads for Point Reyes National Seashore. Again, the Tiger line features provide too much information. You will synthesize the data to present only what is needed. 1. Open the Layers Properties dialog box for the Tiger Edge layer and click the Symbology tab. 2. Select Catagories/Unique Values from the Show window. 3. In the Value field, select MTFCC The newer data from the Census Bureau provides a coded value for each type of feature. The MAF/TIGER Feature Class Code (MTFCC) specifies what type of feature the line represents. You will symbolize major types of road features. 4. Click the Add Values Button. This will open the Add values dialog box. 5. Click the Complete list button. 6. In the list of values, select S1100 and click Add. 7. Repeat steps 3-5, adding S1200 as an additional value. 8. Uncheck the check box next to all other values so they do not display. 9. Double click the symbol for S1100 to modify the symbol as a highway. 10. Double click the symbol for S1200 to modify the symbol as a major road. 11. Click OK to apply your changes and close the layer properties dialog box. 2 8 9 4 11 Helpful Hint In this task, you have opted to only display specific feature types, namely highways and major roads. However, you may wish to add all values, having a distinct symbol for each value. This is done by clicking the Add All Values button on the Symbology tab of the Layers Properties dialog box. Page 3
Exercise 6: Symbolizing your data Symbolizing with charts Before you continue, you will explore some of the specialty tools available for symbolizing. In this task, you will explore some of the chart tools that can be used as symbols on your map. You will initially create a pie chart for racial diversity for each census block. 1. Using the check box in the Table of Contents, turn off the schools and roads layers. 2. Open the layer Properties dialog box for the Census data and click the symbology tab. 3. Select Charts/Pie from the Show window. 4. In the Field Selection window, select all of the ethnic group names. 5. Click the Arrow button to add the fields to the Symbol Field window. 6. Modify the colors used in the pie chart by choosing from the color scheme drop down menu or modify individual symbols by double clicking the symbol in the Symbol Field window. 7. Select an complementary, subdued color for the background. 8. Click the Apply button, and preview your pie charts. You will notice that all of the charts are the same size, you will now normalize the size based on the total 2005 population of the census block. 9. Click the Size button. This will open the Pie Chart Size dialog box. 3 4 5 6 7 9 8 Page 4
10. Click the radio button next to the option Vary size using a field. 11. Select Pop2005 from the drop down menu for your field option. 12. Click OK to close the Pie Chart Size dialog box. 13. Click OK to apply the size change and close the Layer Properties dialog box. You will notice that, when looking at the entire county the number of pie charts is overwhelming and confusing. 13. Zoom to a specific city or neighborhood where each of the pie charts will fit within the census block region. 14. Explore the other Chart types available in the Layer Properties dialog box. As you modify the chart type, your field options will remain. 10 Exercise 6: Symbolizing your data 11 12 Page 5
Exercise 6: Symbolizing your data Symbolize based on numeric range (Quantities) 4 5 7 8 In Exercise 6, you created a new field and ran field calculations to determine a ratio of student age children to the total population. Although a great skill to learn, this is not always needed. When symbolizing you can normalize your value based on another field. You will do that in this task. You will then modify the classification method. 1. Right the Census Block layer name in the Table of Contents and select Zoom to Layer to zoom to the full extent of the layer. 2. Open the Layer Properties dialog box for your Census blocks and click the Symbology tab. 3. Select Quanitites/Graduated Colors from the Show window. 4. In the Values field, select AGE_5_17. 5. In the Normalization field, select POP2005. 6. Click Apply to preview your settings. By default, Arcmap will categorize using a Natural breaks (Jenks) method, and create 5 classes. You will customize these settings. 7. In the Classes drop down menu, select 7. You will notice that additional classes have been added to the Symbol window. 8. Click the Classify button. 3 6 Page 6
This will open the Classification dialog box. On this dialog, your data values are presented in a grey bar graph with breaks indicated with a fine blue line. The break values are also listed in the window on the far right side of the dialog box. 9. Modify the Classification method and preview how each method changes the breaking locations. You can also modify the locations of the breaks by clicking and dragging the blue break lines to different areas on the display or by modifying the values in the breaks value window. 10. When satisfied with the break locations, click OK to close the Classification dialog box and click Apply to preview your settings. 11. Continue to modify the classification settings as needed. You may also need to modify the color ramp so that each area is distinct from its surroundings. 12. Click OK to close the Layer Properties dialog box. Classification method Exercise 6: Symbolizing your data Data statistics Data values displayed in grey Break values in blue Break values also in numeric format Page 7
Symbolizing using multiple field values 4 Exercise 6: Symbolizing your data 7 You have modified the symbology for your roads data as well as for the census blocks. In this task you will modify the symbology for the schools in your county. The schools layer contains many different types of schools. You will display only the Elementary, Middle and High schools in your county. Further, you symbolize the color based on type and the size based on population being served. 1. Using the check box in the Table of Contents, turn on the County wide school layer. 2. Open the Symbology tab of the Layer Properties dialog box for the school layer. 3. Select Multiple Attributes/Quantity by Category in the show window. 4. For Values, select SCH_TYP. This field specifies the type of school. 5. Using the Add Values button, add symbols for Elementary, Middle and High Schools. 6. Uncheck the box in the Symbol window to not show all other values. 7. Modify the colors for each of the school types by double clicking the symbol in the Symbol window. At this point, do not modify the size of the symbols. This will be covered in the following steps. 8. Click the Symbol size button. 3 6 7 5 Page 8
This will open the Symbol Size dialog box. 9. For the Values field, select Pop_Stat_1 in the drop down menu. The higher the number in this field, the smaller of a population center is designed to serve. A value of zero signifies that the population size has not yet been determined. To properly symbolize this, you will flip the symbol size, making the lower numbers have a larger symbol. You will also make the zero values a neutral size. 10. In the symbol Size range fields, specify the range to be from 8 to 2. 11. Double click the symbol for the Zero value and modify the size to 6. 12. Click OK to close the Symbol Size dialog box. 13. Click OK to close the Layers Properties dialog box. 10 11 9 Exercise 6: Symbolizing your data 12 Page 9
Exercise 6: Symbolizing your data Other cartographic considerations Your symbology tasks are complete. As you zoom to the full extent of the map. Here are a few questions to ask yourself in considering the quality of your map. Is the background of your map distracting from the information you are wanting to send? In this map, you added the surrounding counties. This keeps your county from looking like an isolated island. Be sure that the symbology of the background complements the theme of the map and doesn t shout louder than the information you are presenting. Are the colors appealing? Although your map should be presenting information, if the colors are not enjoyable, people will not want to look at it long, and your map will, in the end, fail to send the message that you want to send. Does the color variation complement your message? As you present different colors, be sure that the colors are sending the message you hope to send. Also, if you are wanting to show a sharp contrast, you will want to use two colors that contrast. Does your map present the correct mix between art and science? If your map is too colorful, or too distinct that it dissolves your message, then your map is not successful in presenting information. If your map is too dull that your audience looses interest, then, again, your map is not completely successful. Again, cartography is a mix of science and art and is a skill that will develop with practice. Page 10