CRP 386: Plans and Plan-Making
Census Assignment Tips
Table of Contents
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Trouble-shooting field (column) names in attribute tables (e.g., SF3 tables)
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Problem 1 - field names are changed in the conversion from Excel to dBase to ArcMap
Problem 2 - field names are too long to see when trying to map a value
Trouble-shooting field (column) names in attribute tables (e.g., SF3 tables)
Problem 1 - field names are changed in the conversion from Excel to dBase to ArcMap
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When you are converting data tables between Excel and dBase, you will run into problems regarding field (column) names in the tables. In dBase formats, field names must be 10 or less characters with no spaces or other unusual punctuation. If your field names in Excel are longer than this, they get chopped down in the process of saving to a dBase (.dbf) file.
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When using SF3 data from the Census Bureau, the conversion from Excel to dBase results in the loss of the last numbers of the field name, which is really bad because they identify the different fields. E.g., GCTH9_CO1.C0 becomes GCTH9_CO1, and GCTH9_CO1.C1 also becomes GCTH9_CO1. When you bring this into ArcMap, it tries to help by adding sequential numbers to the field names in order to distinguis them - unfortunately, it adds a 1 to what had been a 0, 2 to what had been a 1, etc. All of which causes total confusion, and makes you understand why it is much easier to buy pre-processed data if possible.
Solution for Problem 1
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Change the field names in Excel before you save as a dBase (.dbf) file. You can use whatever field name makes sense to you as long as you keep it 10 or less characters with no spaces or other funny stuff (e.g., med_HH_inc will work, as will medHHinc).
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While you're at it, you can also delete any fields in Excel that you don't need for data display in ArcMap. Just make sure not to delete the Geo_id field - you need that to make the join to the tracts layer.
Problem 2 - field names are too long to see when trying to map a value
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When you join the newly created .dbf file to a layer in ArcMap, another potential problem occurs. The field names that you see are even longer because ArcMap adds to each field name the name of the table the field came from (either the layer's attribute table or the newly joined table). Click here for example of a joined table showing the census2000_tracts layer joined with a table called finan_housing - you see the end of one table and the beginning of the next table. This addition is only temporary while the join is in place, so your field names have not actually been renamed. Still it can be confusing to look at.
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It becomes even more confusing when you try to create a map, because when you click to choose the value you want to map, the names are soometimes so long, you can't see them in full and so can't see which is the desired field. Oy!
Solution for Problem 2
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I have solved this particular problem by exporting the layer, with the table still joined, to a new shape file. To do this, right-click on the layer name (e.g., census2000_tracts_sf1) and choosing Data - Export Data. This creates a new shape file with the original attributes of the layer and the joined table together in one new permanent shape file (by contrast, a join is temporary). You should name this new shape file something reasonable, e.g., tracts_SF3_income_poverty. Once you do this, the field names go back to what you originally named them and are easier to see. This is not an ideal work-around, but it works.
A few tips about census maps:
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Because tract boundaries are in part set to contain around 5000 people, and so are very close to each other in population, it doesn't make much sense to do a map of total population - there just aren't big differences. It would make more sense to map population density (total population divided by area in square miles), but you do not as yet have an area field to use for this. There is a way, and you will learn it later, but you have enough complications for one assignment!
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Mapping number or percentage of females or males is also not very helpful as the values are around 50% most of the time. It is interesting to find exceptions to this (e.g., where there is a large military base or prison), but these are very rare. So don't make maps of gender unless you have a specific need or purpose.
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Remember, don't try using fill patterns (hatching, dots, etc.) - they are very distracting and hard to distinguish.
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Use a single color scheme (e.g., pale blue to dark blue, white-gray-black, pale red to dark red) - as we said in class there are some other color schemes that work but the safest bet is a very simple color scheme.
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Use the Natural Breaks method of classification unless you really think another method more effectively tells the story you want to tell. But do adjust the breaks to make more sense to a map viewer (e.g., 13.9% might be better set at 15%).
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For now stick with the graduated colors option, again unless you see a pressing need for something else. Other options like graduated symbols or dot density can sometimes be appropriate, but you should wait to use them until you have a better understanding of what impact they convey. Take a look at using charts, like pie charts (e.g., you can show in a pie chart the distribution of vacant, owner-occupied, and renter-occupied units), but again, unless you feel very confident of your design skills, hold off for now. These make good maps in very rare circumstances. Just because the computer can do it, doesn't mean you should use it!
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Manage your white space! The shape of Travis County offers some opportunities for map element placement. You can allow the county to fill the whole page, for example, but still have room to the top just right of center and in the bottom two corners. See example map layout, and note that the map frame has been expanded to fill the whole page, while the other elements are placed within the map frame. This particular example would apply if you were doing one map per page. If you are doing several maps in a page, your solution would be different.
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If you are putting more than one map on a page, some notes to help:
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Here is an example where I have placed all six maps on one tabloid size (11x17 inches) sheet. The map isn't perfect (I should have made the maps themselves slightly larger probably) but you get the idea - Travis County Census Tracts, 2000.
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To make all the data frame panes the same size, hold down the CTRL key and click on each pane in turn - this is the way to select multiple panes. Then with all the panes selected, right-click to get a menu for adjustments. One of the available functions is Distribute and under this you can use the Make Same Size option (see screen print example). You will also see an Alignment function that will help you line up panes.
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Make sure all the data panes are showing the county at the same scale. You have to set the scale for each individual pane but you should do this towards the end of making all the adjustments to your layout, otherwise you might have to set scale all over again anyway. To set the scale for a data frame in Layout View, click on the data frame you are working on, then go to the scale area of the Standard Menu and type in the appropriate scale (I used 1:900,000 for my tabloid sheet with six maps:
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OK, now to the legend!
Bad legend |
Better Legend |
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How to get from here to there...
This is what I do with legends - you can also read up on them in ArcGIS Desktop Help.
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First, when creating the map in the first place, set intelligible breaks and labels for your data - you do both these things in the Layer Properties - Symbology tab, as in the example below (renter occupied normalized by total housing units to show percent renter-occupied) - here I have used the Natural Breaks method but I am in the midst of slightly adjusting the upper break points in each range and applying labels:
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Next create a legend in the layout view (Insert - Legend). I typically accept all of the defaults. This gives you the bad legend but you now have something to play with...
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In the lay-out, right-click on the legend and choose Properties.
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In the Legend tab, I type the legend I want to see on my map, e.g., % Renter-Occupied. Make sure that Show is checked.
(Note: in your title or other text, you should be explaining what the map is in full, e.g., Percent of total housing units that are renter-occupied. With that done, your legend title can be very succinct) -
In the Items tab (still in Legend Properties), first make sure that any items (layers) you don't want in the legend are not showing by clicking on unwanted items under Legend Items and moving them back over to the left)
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Next right-click on the legend item of interest (or the one that is causing problems, in my example the item is the layer census2000_tracts_sf1) and select Properties
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In the Legend Item Properties box, click on the General tab, and uncheck Show Heading. This gets rid of the annoying RENTER_OCC/HSE_UNITS heading
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Another route to modifying the legend is to click on the item as above, then click the Style... button, then click on the various style examples and check the little preview pane. I use the third style down - Horizontal Single Symbol Label Only for the census maps.
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11 February 2004
The School of
Architecture at UT Austin
Comments to: Barbara Parmenter
(bparmenter@mail.utexas.edu