Intro to Atlas GIS 2.0
Mackenzie, Tanjuakio and Sparco
Intro to Atlas GIS 2.0
The first part of this chapter introduces AtlasGIS's page layout and display control functions, and has you experiment with these. The second part introduces methods for selecting specific geographic features and associated attribute records for query or analysis.
First, try displaying a map to familiarize yourself with some basic AtlasGIS functions: File-Geographic-use_As (typed "fga"). You will be asked to choose an existing geographic file, and then name a new copy of that file. Hit the SPACEBAR key to see a pick-list of available geographic files, directories and disks. Use arrow keys or the mouse to highlight the "STATE" geographic file, and hit ENTER to select it. Now you will be asked to name the new copy of this file (e.g., "mystate"); type the new name in the query box and hit ENTER. This new copy will be the active geographic file listed after the G: in the status window at the upper-right corner of the screen. The original geographic file will not be altered.
GIS files typically require substantial amounts of disk space. As you become more confident and less likely to make fatal errors with Atlas, you can work with your original files (Use rather than use_As) to avoid tying up scarce disk space with duplicate working copies of your files. (Note: some of the commonly-used AtlasGIS files on the lab machines are write-protected, so you cannot Use them directly.)
A note about remote drives: If your computer has network access to a remote drive (say, H:) with Atlas files stored on it, you should avoid simultaneously reading from and writing to that drive to avoid file corruption. For example, it would be safest to access H:\AGISDATA\MYFILE via use_As, making a working copy C:\AGIS\DATA\NEWFILE on your local (C:) hard drive. Accessing the original via Use is likely to corrupt the original immediately; accessing it via use_As and creating the working copy on the remote drive will probably yield a corrupt working copy.
Once you have a geographic file loaded and displayed, try these functions:
View-Map-In lets you zoom in in your map. Use your mouse to define opposite corners of a rectangular map area you want to zoom on. View-Map-Pan lets you move around a zoomed-in map (very useful when you're digitizing or selecting small features).
View-Map-Scale sizes the map to whatever scale you specify at whatever center you specify with the mouse. View-Map-Chosen zooms the map so that the view just encompasses all currently selected geographic features.
View-Map-Reset restores the default view of the full map. View-Map-Undo recovers the previous view.
The same view functions are available for any map inset element you have activated, e.g. a detailed (zoom) view of some area of your main map.
Don't confuse map view functions with similar View-Page functions such as View-Page-In and View-Page-Pan, which zoom or pan you around the entire work area (including the title, legends, scale, etc.). View-Page-Maparea makes the map fill the entire page, which is useful for digitizing.
Display-Page-Pagesize lets you alter the orientation and size of your page. The default page size is 11 inches wide by 8.5 inches tall (landscape orientation), with half-inch margins. If you want portrait orientation, switch the width and height values. If you will be printing large-scale hardcopy, set the width and height values accordingly, e.g., B or ledger size paper is 11 x 17 inches; D size is 24 x 36 inches.
Display-Page-Settings brings up the main page control screen. All the elements in the work area are listed: the whole Page, the Map, two Insets, two Thematic Legends, the Layer Legend, Scale and Title.
First, Atlas lets you add one or two map insets to your work area. These are useful when you want a detailed (zoom) view of some portion of your map. By default, Inset1 and Inset2 are set to "Off." Try turning Inset1 "On" in the Status column of the Display-Page-Settings screen, then hit F10 ("done") to close the control screen. You will now see a duplicate of your map in an inset window. First, use Display-Page-Resize to resize the inset window. Then Display-Page-Move to shift its position in the work area. Then View-inset1-In to zoom in to a portion of the map in the inset window.
Display-Page-Settings also lets you control the border styles of elements: you can set Outline Styles to "None" to eliminate element borders and reduce the visual clutter of your work area.
You can rearrange the page elements any way you like with Display-Page-Move and Display-Page-Resize.
Use Display-Title to change the title text, color, font, etc. This menu only supports two lines of title. If you need additional title lines, you can add them with Display-Freehand-Add-Text, and then adjust the font, text height, etc. as desired.
Use Display-Scale to change the display or definition of the map scale element.
Display-Layer-Settings is probably the most frequently-used control screen in AtlasGIS. Note that some columns in this control window which have <<bracketed>> cells, indicating these call up subsidiary menus or control windows. The first column controls the display status (on or off) of each layer in the active geographic file. The second column accesses style settings controls for each layer, including: colors and styles for line features and region feature boundaries, icons and icon sizes for point features, foreground and background fill colors for region features, and relative drawing priorities. Layers assigned higher drawing priority numbers get painted on top of layers with lower priority numbers.
The label settings control the wholesale display of feature labels for any layer. Geographic features may be labeled using any field in the geographic file or current associated attribute file. Labels may be always visible, or (for region features) visible only if they fit within the associated region. Labels may be set to appear only at specified ranges of map scale. They can be offset, tilted, etc.
The Display-laBel menu lets you make final adjustments to the labels of individual features as necessary.
You can save complex layer settings to a layer settings file if you wish.
Try to compose a visually appealing map of the U.S. To begin, use File-Geographic-use_As to load a copy (name the copy whatever you want) of the geographic file STATE which contains U.S. states, interstates and major cities.
1. Use Display-Title to enter an appropriate title, in whatever font, colors and type size you like.
2. Use Display-Scale to change the scale display to suit your taste.
3. Use Display-Page-Settings to eliminate any unnecessary map element borders (boxes around the title, scale, etc,). Also, turn on the "Inset 1" element and turn off the "Thematic Legend 1" element.
4. Use Display-Page-Move and Display-Page-Resize to move map elements around the page or resize them. Try to make the map and inset elements as big as possible, and fit the other elements around them.
5. Use View-inset1-In to zoom in on Delaware in your map inset.
6. Use Display-Freehand to include your name in small type in a bottom corner of your map, perhaps add an arrow from the inset element pointing to Delaware on the main map, and add text notation to the inset element.
7. Use Display-Layer-Settings to change feature display colors, and label each state by name as long as the name fits within the state boundary. Try filling the states with a light grey color (try 10% black background) for contrast.
The Atlas Select menu permits you to choose specific geographic or datapoint features for editing or other manipulation. When you select a geographic feature, if an attribute record in the active attribute file is linked to it, this attribute record is selected as well.
There are various ways to select geographic features:
Select-One and Select-Many ask you to specify which geographic layers you want to select features from, and then let you use the mouse to select individual features in the map area. Selected features are highlighted in blue in the map area. When features are clustered and Atlas isn't sure which feature you mean to select, it highlights a likely choice asks you to confirm or reject that choice. The / (slash) key accesses some useful selection tools, including View-Map-In and View-Map-Pan which let you zoom in on small features and make sure you select the right ones.
Select-Draw lets you draw a circle, box or polygon on the map area, and select all features from the specified geographic layers within that circle, box or polygon.
Select-Layer lets you select all features in a particular geographic layer, or toggle (switch selected to unselected and vice-versa) the features in a particular layer.
Select-Condition lets you select features with attributes meeting a specific condition, specified as a database expression.
Select-Geographic lets you select features which are inside, touching or within a user-specified distance of an already-selected geographic feature or set of features.
Select-Subset selects a subset of a set of already-selected features by condition (e.g., all counties which don't contain a major city and where more than 55 percent of the population is female) or geographic proximity (e.g., all stores located within counties with median housing values over $125,000). When you select a subset by condition, Atlas de-selects all selected features that don't meet the subset condition. If you make a mistake in specifying a subset condition, everything may be de-selected. You can avoid having to re-do complex selections by saving them (Select-File-Save) and recovering them (Select-File-Load).
Note that most select functions, with the exception of Select-Subset and Select-Layer-Toggle, will not de-select features which have already been selected, but simply add to the set of already-selected features.
Suppose you want to create a map of counties in the Northeast U.S. AtlasGIS comes with a "COUNTY" file for the entire U.S. which includes state and county boundaries, interstates and cities with populations of 50,000 or more. First, activate a copy of Atlas's "COUNTY" geographic file (File-Geographic-useAs, name it "JUNK"). Next, activate a copy of Atlas's "CNTYDEM" attribute file (File-Attribute-useAs, name it "JUNKATT"). Then View-Map-In to zoom into the Northeast region showing the states from Maine to West Virginia.
1. Use the mouse to select all 12 states from Maine to West Virginia. The Gsel: entry in the status window will report the number of geographic features currently selected. (Note that the Asel: entry will not show any records from the CNTYDEM attribute file as selected, since this file contains county-level census data but no state-level records.)
2. The COUNTY file has four layers: States (R), Counties (R), Cities (P) and Interstates (L). You would like to include all of these in your map of the Northeast U.S. Select all features (from all layers) located within the 12 states already selected. After AtlasGIS is done testing whether each feature is inside any of the selected states, you should have 706 geographic features (299 county region features, 12 state region features, 196 interstate highway segment line features and 199 city features) along with 299 county attribute records selected.
3. Write these 706 selected geographic features to a new geographic file. Atlas will ask you name this file (name it "NE_US" or whatever else you want), and provide a brief description of it. Then write the 299 county attribute records to a new attribute file. Name this new attribute file "NE_CODEM" or whatever (Atlas adds the appropriate filename extensions). Now close the COUNTY geographic file and CNTYDEM attribute file (File-Geographic-Close and File-Attribute-Close), and activate the new geographic file you just created (File-Geographic-Use).
4. Your new map will look tilted because it retains the projection of the original file (Albers, centered on Kansas). Use File-Geographic-Tools-Project to reproject this to UTM Zone 18. ("UTM-18" is near the bottom of the very long pick-list of available projections; use END and PAGEUP keys to find it quickly.) Try Lat-Long (LL), and note the difference.
Your new map uses Atlas default display settings: typically all region features have brown boundaries, all line features are blue and all point features are red triangles. Use Display-Layer-Settings to improve on this. Make the state boundaries black, with a line width of 20 (the wider lines may not show on the screen, but will on a printout). Disply the county boundaries as dotted black lines. Display the interstates as red lines. Display the cities as blue circles. (Note the other available color, line style and symbol choices.)
You can obtain summary statistics on selected geographic features or their associated attributes using the various selection criteria. Select-Geographic-Near lets you search for and select any features from any layer(s) within a specified radius of any feature(s) selected from an "input" layer.
Suppose you wanted to select and display summary statistics on all counties whose centroids lie within 100 miles of Wilmington, DE. Activate the "NE_US" geographic file and the associated county attribute file. Zoom in (View-Map-In) on Delaware and select (Select-One) Wilmington from the "Cities (P)" layer. Use Select-Geographic-Near, specifying Cities as the input layer, "Selected" only, and "Yes" to Deselect When Done (this will leave just the counties selected, and de-select the Wilmington point feature). Specify "Counties" as the layer to search within a 100-mile Distance to Search, "Centroid" as the Method, then <<Done>>. You should now have 55 counties selected, along with 55 associated attribute records.
Select-Info provides summary statistics derived from the attribute records for these 55 counties: they contain over 17 million people, 51.5 percent of whom are female, etc.... (Pay attention to the description of each attribute field given at the top of the screen: some fields are percents with meaningless sums.)
Load the COUNTY geographic file and CNTYDEM attribute file, or your Northeast U.S. counties geographic file and associated Northeast counties demographic attribute file.
1. How many counties have an interstate running through them? What is the average of the median values of owner-occupied housing units in those counties?
2. What is the average of median housing values in counties without interstates running through them?
3. What is the average of median housing values in counties through which I-95 runs?
4. What is the average of median housing values in counties adjacent to the counties through which I-95 runs?
5. How many cities (populations > 50,000) are located in counties without interstate highways running through them?
6. How many counties without interstates have populations where 15 percent or more of population is 65 years of age or older?
You can merge geographic files to create a single composite file. If you have an active geographic file, File-Geographic-Merge will let you merge files for different geographic areas, or files with different features in the same area into the active file. If you do not have any geographic file active, File-Geographic-Merge will create a new composite file from specified existing files.
Suppose you want to combine three county geographic files of Census tracts in Delaware into a single file. File-Geographic-Close will close your active file. Then File-Geographic-Merge will let you identify the three county files from the pick-list, and specify the name of the new composite file.
When you are merging geographic files, the projection of the active geographic file (or the first file you specify if no file is currently active) becomes the default projection for the composite file; if any other file you specify is in a different projection, AtlasGIS will warn you and convert its projection before merging it.
You can merge attribute files with File-Attribute-Merge, and datapoint files with File-Datapoint-Merge.
Remember that you can only have one geographic file, one attribute file and one datapoint file active at a time. If you need to have more than one datapoint file active at the same time, you can import one set of datapoints as a new point layer in a geographic file. AtlasGIS does not let you readily convert point layers back to separate datapoint files, however.
Remember that GIS files can quickly get very large and unwieldy. (The main reason AtlasGIS uses separate geographic and attribute files is to keep file sizes manageable.)
Merges can take lots of time and RAM, and you should develop a strategy for efficient merges of large files. Merging large files into small files is generally quicker than merging small files into large files. You may opt to select subsets of relevant records from each source file, write these to new files (File-Attribute-Tools-Write) and then merge these subsets to create a new composite file.
More generally, it is good practice to keep your file sizes small so that (a) routine operations on extraneous records don't tie up your computer for excessive periods of time, and (b) you don't waste disk space and have jobs crash on "Disk Full" errors. Keep track of duplicate files created with use_As and delete them (at the DOS prompt--you can't do this within AtlasGIS itself) when you no longer need them. Remember that an Atlas geographic file is actually multiple files with the same name and different extensions. Use a wildcard extension to erase all the files associated with a particular geographic file.
Keep files small by eliminating unnecessary detail in features, deleting unneeded features, and deleting unneeded layers.
To eliminate unnecessary detail in a region or line layer, use Operate-Generalize. This algorithm eliminates vertices which have little or no influence on the shapes of features. (This is described more fully in Chapter 4.)
To delete a feature from a layer in a geographic file, first select it. Edit-Geographic-Delete-Delete will delete both the geographic feature and its associated attribute record (if any). Edit-Geographic-Delete-Partial deletes geographic features but not their associated attribute records. If you make a mistake, you can recover the last-deleted feature(s) with Edit-Geographic-Delete-Undo.
Whenever you delete a large number of unwanted features, you should then compress (File-Geographic-Tools-Compress) the geographic file to actually erase the unwanted records. Otherwise they are simply tagged as "deleted" but still remain in your geographic file, and may still bog your processor down.
To delete a layer from a geographic file, you must first select (Select-Layer-All) and delete (Edit-Geographic-Delete-Delete) all the features within that layer. Once the layer is empty, you can delete it with Edit-Layer-Delete. Note that its entry in the pick-list will specify the layer type with an asterisk (R*, L* or P*) which indicates the layer is empty. Atlas won't let you delete a layer which is not empty.