ArcMap is an easy-to-use program to display map data, symbolize it in useful ways, and output it to common, shareable file formats.
This tutorial will guide you through constructing, coloring, and saving a simple map using ArcMap, the primary component of ArcGIS, using prepared data. In the process of doing this, you will become familiar with some of the menus and procedures you would use to create maps using your own resources.
Since this tutorial will be using specific maps and data, the first step is to make your own copy of the tutorial data. First go to the network drive K: (aka \\Software\Winsoft), open the folder Maps, and then open the folder Introduction to GIS. Drag the folder constructingmaps and its contents to your network drive U: (e.g. into the folder My Documents), or the local drive C: (e.g. onto your Desktop). Since some but not all of the ArcGIS programs have trouble handling names with spaces or special symbols, do not rename the folders unless necessary.
Note that many of these files have the same root name, e.g. states; this means that they must all stay together to work properly.
Each such set of data is known as a shapefile (although only one file has the extension .shp), and is one of the basic data formats that is understood by ArcGIS.
The main ArcMap window is divided into two panes:
The larger pane on the right is the map display area. You can display geographic data here by adding it with the yellow-and-black button Add Data. It’s located in the Standard toolbar, which is usually docked just below the menus in the ArcMap window.
Prepared data is ready to use with ArcMap, without the need to first establish its geographic basis.
A map of the United States including Alaska and Hawaii should now appear in the map display pane. Data such as states that are displayable geographically are called layers, because they overlay each other like transparencies when you add them. Maps can display several different kinds of layers: points, polylines, polygons, images, and others. The layer states consists of polygons defining the boundaries of the fifty states. Each of these polygons is called a feature of the layer.
The layer’s name will also be listed in the pane on the left, which is called the Table of Contents. By default its name is the data file’s root name, but it can be easily changed by cllcking on it and typing.
The Table of Contents provides three views of your data. The primary view is List by Drawing Order, which shows just the simple names of data layers, corresponding to what is visible (or potentially visible) in the map pane. The secondary view is List by Source, which lists the full path names of your data files. In addition to data layers, it also shows data you’ve referenced that is undisplayable, such as tables of additional data. Usually you’ll want to stay in the Drawing Order view. The third view, Selection, is a topic for another day.
Experiment: Click on the tabs Display and Source to observe how the view of your data changes.
Before we proceed any further, it’s a really good idea to save your map.
ArcMap documents preserve your current arrangement for use at a later time, and are especially useful after the occasional ArcMap crash.
In addition, ArcMap is aware of the location of a saved map, establishing it as the Home folder so that related files are easy to find.
You’ll therefore want to continue to save them on a regular basis, for example every time you’re satisfied with the current view.
ArcMap documents do not actually contain the data you add to them, such as the layer states. Instead, they contain pointers to your data, as well as information about how to display them. That’s why it’s a good practice to keep them together, unless the data is in a standard, shared location such as an archive.
Because ArcMap documents only contain links to your data, another good practice is to make those links relative to the map document. For example, the data might be referenced as being “in the same folder as me” rather than being “in the folder C:\Documents and Settings\username\Desktop\constructingmaps”. Either of these is known as a path to the data; the former is called relative while the latter is called absolute. Relative paths will facilitate moving the folder containing your map file along with all the files linked to it to another location.
Note that you can only open ArcMap documents by double-clicking on them in the Windows Explorer, or by opening them from within ArcMap through the menu File and the menu item Open (or clicking on the button Open). They may not be added to a map using the button Add Data, which is reserved for the different pieces of data that make up a map.
The primary toolbar is called Tools, and it contains the buttons listed below. They provide quick ways to zoom in and out, pan across the map, restore a map to its full extent, and return to previous views of the map:
The toolbar is shown above docked between the two window panes, but may be located in some other position when you open ArcMap for the first time.
Experiment: Locate the toolbar and drag it into position between the two panes (unless you prefer it somewhere else).
Experiment: Try zooming in and out of the map, panning, and using the full extent button to return to the original map view. Also try using the back and forward buttons to move along the sequence of views you’ve created.
We’ll talk about the other tools later.
The degree to which one has zoomed in to or zoomed out from the map is commonly expressed by comparing a distance on the map to the same distance in the real world. So, for example, the distance from New York to Los Angeles is about 6 centimeters in the computer view above, but roughly 4,000 kilometers in real life. Since 6 cm = 0.00006 Km, we can calculate a ratio of these two numbers that doesn’t depend on units, 0.00006 Km : 4,000 Km = 1 : 70,000,000. This ratio describes what one map unit corresponds to in the real world, and is called the map scale.
ArcMap displays the current map scale in a text field / menu at the top of the screen just to the right of the button Add Data:
Intially the scale for your map will be around 1 : 100,000,000, depending on the size of the map display pane. As you use the zoom buttons in the Tools toolbar, the scale adjusts automatically. It’s also possible to change the map scale by clicking and typing directly in the text field, or by clicking on the adjacent pop-up menu button and choosing from a list of common values.
Experiment: Observe how the map scale changes as you zoom in and out of the map. Try changing the scale by typing a number in its text box, and by choosing a value from the menu.
Note that as you decrease the second number in the map scale ratio, the scale increases. Cartographers therefore use the following terms to describe scales:
When you add a map layer, you will also bring along an attribute table describing the individual features of the map. For example, every state in the map has a name, and we may want to label them, so we need to know how those names are associated with the polygons.
Shortcut: you can also open a layer’s attribute
table by holding down the
In this table, every feature of the layer is listed in its own row or record. Each column or field represents a different attribute of these features. So, in this case, we see each state name on a different row, along with its population in 2000 and 2005, its federal information-processing code, etc.
Every attribute table will begin with the two structural fields FID and Shape. The first is a Feature Identifier that will always be a unique number to distinguish one feature from another. The second is a summary description of the geography of this feature; hidden behind the text “Polygon” there’s a lot of information about how to draw the lines that comprise it.
All other fields are optional, but their presence is important to enable the true power of GIS. These fields are usually one of two types:
Note that sometimes fields appear to be numeric but in fact are text, e.g. STATE_FIPS, because they are stored as a sequence of individual digits.
The features in a table are often in a random order. However, you can compare them more easily with each other by sorting them by any one of the attributes in the table.
Note that the column will sort itself in ascending order, from A to Z.
that now all of the records are sorted according
to the first field,
and within each group the records are sorted
by the second field.
Note that all of the data in a row stays together, even though you’ve sorted on a single column (something that doesn’t automatically happen in a program like Excel); this is a common feature of a database.
Experiment: Sort the data by different fields in the table.
Once you have found a feature in a table, you can locate it on the map in a few ways.
The most common is to select it, but you can also flash it and zoom to it.
The feature is now selected , and its record will be highlighted in an aqua color.
In addition, the feature will be highlighted in the same color on the map itself; you may have to scroll, zoom, and/or move the attribute table around to see it.
The information in the attribute table can be used in a more focused way to explore map features.
When you don’t have the attribute table open, and you recognize features on the map, you can also select them using the tool Select Features.
When you don’t have the attribute table open, a quick way to get information about a particular map feature is to use the tool Identify.
With a single layer on the map, these options all have the same effect; there will be more about multiple layers later.
More often than not you won’t recognize a feature on the map, but you can find it without going into the attribute table using the tool Find.
With a single layer on the map, these options all have the same effect; there will be more about multiple layers later.
There is, of course, a more general way to identify features on a map, and that is by labeling them on the map itself.
Every map you’ve ever seen probably includes labels that give names to the features on the map.
ArcGIS can label a layer with any of the data in its attribute table, and it will intelligently position them to avoid overlap with other layers’ labels.
The general properties of a layer, such as labeling and the data source, are controlled through the dialog Layer Properties, which you will see a lot of from this point onward.
Shortcut: you can also open a Layer Properties
dialog by double-clicking on the layer’s name
in the Table of Contents.
Zoom into the map to verify that the labels you’ve added appear at an appropriate scale.
Right-click on the map layer again and select Properties to bring up the Layer Properties screen. Now select the Symbology tab.
At present, the map is colored using a single color (symbol) for every feature (state polygon). If we simply wanted to change this color, we could click on the colored rectangle and select a different color. However, what we want to do is color the states different colors. To color the states different random colors, select Categories (which will bring up a new screen), set the Value Field to STATE_NAME--because we want to give different colors to states with different names. Then choose a Color Scheme on the right that consists of patches of distinct colors.
Click the Add All Values button and OK. Each state will now be colored by one of the colors from the scheme you chose. You can go back to the original single color for all states through the Symbology tab by selecting Features then Single Symbol then OK.
Right-click the states layer, select Properties and then the Symbology tab. Select Quantities on the left.
Begin by selecting the quantitative variable for coloring the map as the Value in the Fields section.
Coloring a map using a quantitative variable is more complicated than coloring it using random different colors. There are three basic choices to make:
Such a map is sometimes called a heat map because of its common use to describe temperature, though usually with a blue-to-red (cold to hot) color ramp.
ArcMap will by default use five categories and the natural breaks method for dividing the values into five categories. The natural breaks method tries to draw the lines between categories of values where they naturally break. If you want more categories, you can easily change the number. Usually between five and eight categories works reasonably well. If you use too many categories, the color values may be difficult to distinguish.
To use a different method of classifying values, click the Classify button over on the right side of the screen.
The quantile method creates categories with near-equal numbers of features in each. If we use it to create five categories of states and there are 51 states (50 states and the District of Columbia), we will get categories that each contain ten or eleven states. The equal-interval method divides the values into categories whose value ranges are the same. Choose one of these methods and click OK on this screen and then on the Layer Properties screen. The map will be colored--or symbolized according to the choices you made.
In many cases, instead of coloring a map with a simple demographic field such as “population 2000” or “people over 80,” you may want to use the ratio of a field like this to another field, typically either a total field--for proportion of the total population over 80--or an area field--for population density. This is done by specifying that field as the Normalization field
Both the classification method and normalizing your data can make major changes in the way your map looks and in the way it is interpreted by someone who neglects to read the legend. It’s important to make these choices based on an understanding of the data, with an eye on establishing visual contrast between different data groups.
Once you have colored a layer in a particular way, it’s sometimes useful to save that configuration for future use, such as in another map. A layer document stores a reference to a data set and how it’s currently symbolized. It can be added to a map just like the plain data set.
One of the most powerful features of ArcGIS is its ability to display multiple map layers at once, much like a set of transparencies allows different views to be displayed together in many combinations. To see how this works, we’ll add more and different types of data to your map, beginning with the plain states file you loaded earlier.
Exercise: Comparing Different Symbolizations of the Same Data File
Next we’ll add a different type of data, a set of points:
Exercise: Adding and Symbolizing a Point Layer
The previous step only allows you to select a uniform symbology for the points in a point layer. Like polygons, it’s also possible to vary the symbol based on values in the layer’s attribute table, but in several unique ways such as changing the symbol size.
We’ll add one type of raster image, representing elevation. It will come from a local repository of map data that we maintain here at Amherst College.
A lot of geographic data is available from government, commercial, and other sources, often in a ready-to-use format.
Often you’ll want to provide background for your data, such as streets or terrain, and not have to worry about constructing it yourself.
The company that makes ArcGIS, ESRI, provides a large number of basemaps through Internet servers, which you can easily add to your ArcGIS map.
Basemaps are relatively easy to add ArcMap, though it’s best to first add your own data to establish its view and ensure a good choice of background. Then:
ArcGiS Online (www.arcgis.com) is a source of geographic data in formats that are ready-to-use with ArcGIS “Desktop”.
It has datasets provided by ESRI (in particular the same basemaps as above, and others that sometimes duplicate what’s in K:\Maps), as well as many that are contributed by others.
ArcGIS Online (www.arcgis.com) can be accessed both from within ArcGIS Desktop and, more conveniently, from any web browser.
You can click on the titles of these data sets to get more information about them, e.g. their size, author, and any restrictions on their use.
As with basemaps, the drawback to using an Internet server as a data source is that they can sometimes be unavailable or slow to load; you may wish to turn them off until you are ready to publish your map.
It’s always worth searching the Internet for geographic data.
Much of this data must be converted into a format that ArcGIS can properly display, and working with such data will be the topic of the next few sections.
However, many sets of data are “prepared” data, i.e. they are ready to be loaded into ArcGIS and immediately displayed.
Commonly such data would be labeled as shapefiles, though they are likely to be packaged as a .zip archive that Windows will automatically open.
Another relatively new format is the geoTIFF, a standard TIFF image that’s been enhanced with geographic information.
Experiment: Try doing a web search for data on a subject you are interested in, and include a keyword such as shapefile or geoTIFF; you might very well have some results.
The ArcGIS software is not available to most people, so its documents are not easily sharable. However, there are a number of different ways to save sharable maps depending on the purpose you have in mind. You can print on paper, create an image, create a PDF, or export it to the free applications Google Earth or ArcReader.
Cartography describes the clear, elegant, and even artful design of a map.
With an appropriate choice of content, structure, symbology, and labels, a map can speak volumes while still being easy to read and understand. A map that is just thrown together may be helpful to the author, who knows what to look for, but could be confusing and quickly ignored by an intended audience.
Entire books have been written on designing good maps. In lieu of reading one of them, here are some important considerations to keep in mind when preparing your maps for sharing:
When you publish your map to static formats such as paper, digital images, or PDF, you’ll need to define a size for the output, which you can think of simply as the paper size. Menu File > Page and Print Setup..., and proceed in the usual way to choose Printer, Paper Size, Paper Orientation, etc. In addition, you’ll probably want to check the box Use Printer Paper Settings, since that is usually a good size for sharing.
To see how your map will look on the printed page, go to the View menu and select Layout View.
This displays the map to fit inside the margins of the paper type chosen. You can change the margins by clicking on them and dragging one of the blue boxes to a new position. Note the thin gray dotted line; it shows the actual limits to printing on the paper size for the printer you’ve chosen.
The map as displayed in the margins is the same one you’ve chosen in the data view, no matter how big or small the margins are. You can use the same tools in the toolbar Tools to change the relative size and position of the map within those margins. Important: in the Layout View, you should have access to the toolbar Layout, which provides similar tools that reference the paper rather than the map with them you can zoom into the paper without changing the size of the map relative to the paper.
Before sharing your map, it’s a good cartographic practice to add a title, a legend to describe the different layers, a north arrow to show directions, and a scale bar to show the map scale:
If necessary, resize the margins around the map to fit these new additions.
ArcMap can have multiple data frames defined in its Table of Contents, but only one of them can be displayed at a time in the Data View.
However, layouts can display the maps from all frames at once, for example to show an overview map in an inset box.
The most basic way to share maps is to save them in one of the file formats commonly found on the Internet.
Go to the menu File and choose the menu item Export Map.... Then navigate to the folder in which you want to save the map.
If your intent is to use the map on a computer, such as in a web page or a PowerPoint presentation, where printing is a secondary consideration:
Choose an image resolution of about 100 dots per inch (dpi), good for display on most computers.
If your intent is to use the map in a paper or a poster that will be printed, for example with Microsoft Word or Adobe InDesign, you will want to save it in an image format that preserves lots of detail;
If you would like the map to be a stand-alone document, then the Acrobat format
Experiment: Try producing all three of these file formats, and compare them. In the PDF document, note the tab on the left called Layers; click on it and then click on the “eye” icon next to one of your layers, and observe what happens.
The free application Google Earth has become very popular, as it provides imagery of the Earth’s surface (taken from airplanes or satellites) in an easy-to-access format if you have an internet connection.
It’s also a lot of fun to use, as you can zoom around the Earth and view it from different perspectives, including terrain and buildings in 3D!
ArcGIS is a useful program to create additional layers that can be viewed in Google Earth.
Exporting to Google Earth makes use of a special geoprocessing tool, an extra program that transforms geographic data into new formats from which additional information can be extracted.
Geoprocessing tools are stored in a collection called ArcToolbox.
The next two procedures are preliminary steps useful for most geoprocessing activities.
By default geoprocessing tools run in the background so that you can continue using ArcMap for other things, but it’s harder to monitor and there can be occasional failures that don’t otherwise occur. So until you’re used to these tools, it’s better to run them in the foreground, even though it will then be the only thing that ArcGIS is doing.
The majority of geoprocessing tools can be found in ArcToolbox, a large collection of “plug-ins” for ArcGIS.
Google Earth uses a geographic format known as Keyhole Markup Language, KML for short, which is sometimes compressed to a smaller size using ZIP compression to produce a KMZ file. ArcToolbox provides tools to export both individual layers as well as entire maps.
It is also possible to create an interactive map that allows the viewer of the map to explore it by zooming and viewing attributes, very similar to what you have been doing already with ArcMap.
Such interactive maps use the free program ArcReader, though it’s only available for Windows.
Creating an ArcReader map is described in a separate section on using ArcPublisher.
If you are interested in applying what you’ve learned to some slightly different kinds of maps, here are some additional exercises. They use map files in the exercises folder in the Introduction to GIS folder.