Lab 2: Getting Data into ArcView

 Table of Contents

 

1.       Goals of this lab

2.       Data formats

a)      Feature data sources

b)      Image data sources

3.       Feature types

c)       Point features

d)      Line features

e)      Polygon features

4.       Exercises

f)        Add themes to a view

g)      Understand theme tables

5.       Lab summary

 

 1.       Goals of this lab

The heart of any GIS project is data; in particular, spatial data. It's data, after all, that you analyze, compare, extract, and present in some way. This lesson covers the following:

  • how feature and image data are structured
  • how to choose the appropriate feature type
  • how to add themes to a view document

how feature themes use tables to store attribute data

 2.       Data formats

 

In ArcView, the spatial data for themes falls into three major categories: feature data sources, image data sources, and ARC GRID data sources. As you will see, you can query and manipulate feature data source themes in many ways, whereas image data source themes can only be displayed.

 

 Views showing feature data (top), image data (middle), and grid data (bottom).

 

a)      Feature data sources

 

Shapefiles are ArcView's native file format for geographic features and attribute data. Shapefiles generally draw faster than other theme sources and you can edit them (move, reshape, add, and delete features and change attribute values) to reflect changes in the source data.

Any of the feature data sources ArcView supports can be converted to a shapefile and then modified. Later in this course, you will learn how to create and edit your own shapefiles.

  

A shapefile being added to the view.

 

ArcInfo stores sets of features and their attributes in its own format, called a coverage. A coverage can be represented as a theme in ArcView. Some coverages contain more than one type of feature; however, ArcView requires a separate theme for each feature type.

In the example below, the county coverage contains a set of point features (labelpoint), and two sets of different polygon features (region.cnty and polygon). Later, you will learn different ways of displaying and manipulating these feature themes.

An ArcInfo coverage being added to the view.

ArcView can read feature data stored in any of the following formats: shapefiles, coverages, dBASE tables of x,y coordinates, text files of x,y coordinates, and CAD drawings. (To access a CAD drawing, you must first install ArcView's optional CAD Reader extension.)

  

A table containing x,y coordinates (an event table) was used to create the Lights theme.

 

b)      Image data sources

ArcView can read many image formats as well as ArcInfo's raster data format, called a grid. The ArcView Spatial Analyst extension allows you to access and manipulate ArcInfo grids and perform complex spatial modeling and analysis on them.

Image themes do not have attribute tables, but you can still manipulate their display with the Image Legend Editor.

Image theme formats supported by ArcView are TIFF, TIFF/LZW, ERDAS, BSQ, BIL, BIP, RLC, and Sun rasterfiles. Supported image data sources include satellite data, digital aerial photographs, and scanned data such as base maps.

  

Sources of images include aerial photography and satellite imagery.

3.       Feature types

In ArcView, geographic data is grouped into themes that are displayed within a view. A theme is a distinct collection of geographic features represented as points, lines, or polygons.

  

Here, you see a view containing point, line, and polygon themes.

 

 

a)      Point features

 

Point features represent spatial data existing at a single location, such as light poles, cities, homes, or wells. (Only the point theme Lights is visible in the view below. All other themes are turned off.)

 

A point theme representing representing the location of light poles.

 

Points represent objects that have discrete locations and are too small to be depicted as areas. Points are stored as a single pair of x,y coordinates.

A point is a combination of two numbers used to represent either a planar (x,y) or spherical (longitude-latitude) point.

 

 

b)      Line features

 

Lines represent linear features, such as water lines, sewer lines, highways, rivers, and local streets.

Lines represent objects that have length but are too narrow to be depicted as areas. A line is a set of ordered x,y coordinate pairs that, when connected, represent the linear shape of a line feature.

The view below shows two line themes: Water Lines and Sewers.

 

Two line themes are shown in this view: Water Lines and Sewers.

c)       Polygon features

Polygon features represent enclosed homogeneous areas or regions. A polygon is a series of line segments connected to form an enclosed area. Examples of polygon features are buildings, land parcels, and sales territories and counties, states, and countries. Polygons represent objects too large to be depicted as points or lines.

In this view, buildings and zoned land lots display as polygon features.

 

4.       Exercises

 

a)       Add themes to a view

 

Suppose that you work for the City Maintenance Department, which plans to add some utilities and upgrade others in a recently renovated part of town. You've been asked to create a map showing the existing utilities to use for planning the additions and upgrades. There is currently no single map that shows all the utilities. Your task is to locate the necessary data sources and add them to a view as themes so you can display them together.

 

Step 1   Start ArcView

If ArcView is not running, start ArcView. If the Welcome to ArcView GIS dialog appears, click Open an existing project and click OK.

If the dialog doesn't appear or if ArcView is already running, from the File menu, choose Open Project.

Navigate to the lab 2 folder and open the ArcView project Lab2a.apr.

Because no views have been created yet, you see an empty Project window.

 

 

Step 2   Create a new view

With the Views icon highlighted, click the New button (or, double-click the Views icon).

A new, empty view window, View1, opens. You can resize and reposition this window anytime you need to.

The gray area on the left side of the view is the Table of Contents. It's empty now, but when you add a theme to the view, the theme's name, the symbol used to draw it, and a check box indicating whether it's currently displayed will appear in the Table of Contents.

 

 

 

Step 3   The Add Theme dialog

From the View menu, choose Add Theme. The Add Theme dialog displays. Navigate to the lab 2 folder in your exercise data folder. ArcView lists the geographic data sources available in this directory.

 

 

When Feature Data Source is selected in the lower left dropdown list (Data Source Types), only data sources containing features (i.e., points, lines, polygons) are listed.

You see four data sources: bldgs, lights.shp, sewers, and waterln. The first of these, bldgs, is an ArcInfo coverage containing more than one type of feature. It appears with a folder icon in the list. Later, you'll open the folder to see the feature types.

The second data source, lights.shp, is an ArcView shapefile (.shp is the default file extension given to ArcView shapefiles). The other two data sources are ArcInfo coverages.

 

Step 4   Add a theme to the view document

Now, you'll add a theme from the Drinkingwater data source.

Double-click Drinkingwater to add it to the view as a theme. The theme's name and a symbol appear in the view Table of Contents.

Your view now contains one theme, Drinkingwater. By default, ArcView doesn't draw the theme. To display the theme, turn it on by clicking its check box.

 

 

 

 

ArcView draws the features in the theme (lines) using the current symbol. When you add a theme to a view, ArcView randomly assigns a color to the theme. Therefore, the Waterln theme may be a different color in your view.

Turning a theme on simply allows it to display. A theme doesn't have to be turned on for you to perform ArcView operations on it, and turning a theme off doesn't remove it from the view.

Step 5   Add other themes to the view document

Next, you'll add themes based on the bldgs, lights.shp, and sewers data sources.

Click the Add Theme button  to display the Add Theme dialog again. Navigate to the lab 2 folder.

You see the same list of data sources.

Step 6   Select several themes in the Add Theme dialog

Click once on the bldgs folder icon to open it.

You see two feature types listed, polygon and labelpoint. ("Polygon" is the ArcInfo term for a two-dimensional feature. A "label point" is a point that identifies a polygon and shares all its attributes.) You want to create a polygon theme to represent buildings, so you'll choose the polygon data source.

Click once on bldgs to highlight it. Hold down the Shift key and click once on sewers. Both data sources are highlighted.

 

 

 

Step 7   Add the themes and turn them on

Click OK to add the two themes to the view. Click on the checkbox next to their names to draw each theme.

Your view now contains three additional themes: the Sewers theme containing line features (which has not been turned on), the Lights.shp theme containing points, and the Bldgs theme containing polygons.

 

 

Step 8   Select an image data source

Now you can use these themes to plan for the utilities upgrade. But first, you'll add an aerial photograph of this part of the city to the view as a backdrop.

Click the Add Theme button. Navigate to the lab 2 folder. Click the dropdown arrow for the Data Source Types list, then click Image Data Source.

The aerial photograph image source appears in the list on the left side of the dialog. The .bil ending indicates a type of image format.

 

 

 

Step 9   Add the image to the view and turn it on

Double-click airphoto.bil. ArcView adds the aerial photograph image to the view. Click the check box for the Airphoto.bil theme to turn it on.

ArcView draws the photograph as a black and white image in the view.

The image draws on top of the other themes. That's because ArcView first draws the theme listed at the bottom of the Table of Contents, then draws each theme listed above it. Thus, the Airphoto.bil theme draws last. You can change the drawing order by dragging themes up or down in the Table of Contents.

 

 

Step 10   Make the image theme active

You want the image to display in the background (behind the other themes) so you'll drag it to the bottom of the Table of Contents. To do so, you must first make the Airphoto.bil theme active. Notice that the Zoning theme is currently the active theme.

Click once on the Airphoto.bil theme in the Table of Contents to make it active. Now it appears raised in the Table of Contents.

Step 11   Change the theme draw order

Click the Airphoto.bil theme's name (or the raised gray area surrounding it), hold down the left mouse button and drag to the bottom of the Table of Contents, then release the button.

ArcView draws the image theme first this time, then draws all the other themes on top of it.

  

Step 12   Close the project

You'll close the project without saving.

From the File menu, choose Close All. Again from the File menu, choose Close Project. Click No when you're prompted to save your changes.

You can see how easy it is to create a view and add themes to it from a variety of data sources. Once you've added themes to a view, you can change the appearance of the view by turning themes on and off and by moving themes up and down in the Table of Contents.

If you want to go on to the next exercise, leave ArcView running. Otherwise, choose Exit from the File menu to close ArcView

b)       Understand theme tables

When you add a theme based on a feature data source, a theme attribute table (or simply theme table) is also added to the project. A theme table contains descriptive information about the features in the theme. The theme table is formatted in rows and columns, called records and fields, respectively. Each field contains all the values for an attribute; each record represents a single feature in the theme. Because attributes are linked to the features they describe, you can access them by clicking on a feature in the view, or you can find a feature in the view by clicking on its record in the table.

The City Maintenance Department has decided to dig trenches for sewer lines on some of the properties. Your task is to retrieve the address information for these properties so notification letters can be sent to their owners. The Bldgs theme attribute table contains the address information you need. You'll make this theme active, then open its attribute table.

Step 1   Open the project 

Start ArcView if it is not already open. From the File menu, choose Open Project and navigate to the lab 2 folder and open Lab2b.apr.

When the project opens, you see a view with four feature-based themes and an image theme in the background.

 

Step 2   Make a theme active

Click on the Zoning name or its legend symbol in the Table of Contents to make it active.

The theme appears raised in the Table of Contents.

 

Step 3   Open the theme table

Click the Open Theme Table button  on the View button bar.

A table window opens containing the attributes of the Zoning theme. When the table opens, you see the first four fields: Shape, Area, Perimeter, and Bldgs#. The Shape field tells you the type of feature (i.e., point, line, or polygon) the theme represents.

The table also contains addresses and owners for all the buildings in the theme. To see them, you'll use the scrolling bars.

 

Step 4   Explore the table

Using the scroll bar at the bottom of the table, scroll to the right.

The address information is stored in the Address, City, State, and Zip fields; the owner names are stored in the Owner field. (Later, you'll resize the table so you can see these fields at the same time.)

You know that the city plans to dig trenches for sewer lines on the properties of the large buildings along the left side of the view. You'll select these buildings by clicking on them in the view.

 

Step 5   Resize and reposition the view and table documents 

Before you select the buildings, you'll resize and reposition the view and table so you can see both of them at the same time.

Make View1 active by clicking on its title bar. Move it to the upper left corner of the ArcView window, then resize it so that it fills the upper portion of this window.

Make the Attributes of Bldgs table active. Move it to the lower left corner of the ArcView window, then resize it so that it fills the lower portion of this window.

 

 

Step 6  Change the table display

You'll change the table display to show the address and owner information.

If necessary, use the scroll bar at the bottom of the table to scroll to the right until you see the Address and Owner fields.

Step 7   Use the Select Feature tool

Now you'll use the Select Feature tool  to select the large buildings along the left side of the view.

Make the view active by clicking on its title bar. On the View toolbar, click the Select Feature tool, then click on the large building in the upper left corner of the view.

The building highlights in the view and its record highlights in the table. ArcView scrolls the table so the highlighted record displays at the top of the table.

Step 8   Select more than one feature

 

 

The first building is selected. Now you want to highlight the rest of the large buildings along the left side of the view.

Hold down the Shift key, then click on each of the other large buildings along the left side of the view.

ArcView selects and highlights the buildings (there are four in all) in the view and their corresponding records in the table.

 

Step 9   Promote the selected theme attribute table records to the top

  

Because the table is large, you can't see all of the highlighted records. To see the highlighted records together in the table, you'll use the Promote function.

Make the table window active by clicking on its title bar. Click the Promote button  on the Table button bar.

The highlighted records display at the top of the table.

 

The highlighted records contain address information for the selected buildings. This information can be used to notify owners about the city's plans to put sewer lines on their properties.

Step 10   Close the project

 Close the project without saving. From the File menu, choose Close Project. Click No when you're prompted to save your changes.

 

By selecting features in a view, you can access their attributes in the theme table. You'll learn other ways to select features and access information about them later in this course.

If you want to go on to the next lesson, leave ArcView running. Otherwise, choose Exit from the File menu to close ArcView.

 

 5.       Summary

 Data is a very important part of any GIS project. There are three main categories of spatial data that you can use with ArcView GIS: feature data sources, image data sources, and ArcInfo grid data sources.

Shapefiles are ArcView's native file format for geographic features and attribute data. Shapefiles display faster than other data sources and are editable. Other supported feature data sources, such as ArcInfo coverages, can be converted to shapefiles and then edited.

ArcView supports TIFF, TIFF/LZW, ERDAS, BSQ, BIL, BIP, RLC, and Sun rasterfile as image theme formats. Sources of image data include satellite photos, digital aerial photographs, and scanned maps. Image themes do not have attribute tables and they cannot be edited in ArcView (you can, however, modify their display with the Image Legend Editor).

Point, line, and polygon are the three types of feature themes. Points represent objects as a single pair of x,y coordinates. Lines represent features that have length but are too narrow to be depicted as areas--a line is a set of ordered x,y coordinate pairs. A polygon is a series of line segments connected to form an enclosed area.

Adding data to an ArcView project is quite simple. When you want to add feature and image themes to a view, you open the Add Theme dialog, select the appropriate type of data source, then navigate to the data file on your computer or network. The data is added to the view as a theme. To display it, simply check the box next to its name in the view Table of Contents.