ArcView Concepts and Overview, October 18-20, 2001


	Back to GIS and Permit/Use Mapping Development ArcView Concepts and Overview, October 18-20, 2001 Desktop GIS Fundamentals Desktop GIS Features Attributes Themes Spatial Data Referencing Spatial Data-Understanding Map Projections Map Scale and Accuracy Detail--Determining What is Important Scale--Understanding Why Different Datasets Don't Match Up Large Scale Maps Small Scale Maps Map Accuracy How to Create Good Spatial Data Overview of Data You Can Use in ArcView Spatial Data Tabular Data Hot Linking to Other Data Sources ArcView's User Interface The Project Window View, Table, Chart, Layout, and Script Windows Menu Bar Button Bar Tool Bar The Table of Contents Creating and Using Maps What is a View? What is a Theme? Working with tabular data What is a Table? Sources of Tabular Data Attribute Tables of Spatial Data Joining Tables Linking Tables Laying out and printing maps What is a Layout? Printing Layouts Customizing ArcView Extensions Desktop GIS Fundamentals Desktop GIS represents the real world on a computer in the same way that maps represent the world on paper. However, desktop GIS has power and flexibility that paper maps lack because GIS provides an almost unlimited amount of information about what can be seen on a map. GIS stores all the information about map features in a GIS database and links features on the map to the information about them. Features: Because features on maps are organized according to relative position or location, maps are good for showing the relationships between feature locations. These relationships are called spatial relationships. To represent real-world objects, maps use three basic shapes, points, lines and polygons (areas). Points represent objects that have discrete locations and, depending on the scale of the map, are considered too small to be depicted as polygons. Lines represent objects that have length but, again depending on mapscale, are too narrow to be depicted as polygons. Polygons, or areas, represent objects too large to be depicted as points or lines. Since shapes alone do not give enough information about a feature, maps use graphic symbols and text labels to help identify features further. Attributes: The information that GIS stores about map features is referred to as attributes. Attributes include a wealth of information about a feature, including its name, length or area, ownership, use, etc, to list but a few. GIS formats attributes in rows and columns, and stores them as tables. Each column stores a different attribute, and each row relates to a single feature. The link between map features and their attributes is the basic principle behind how a GIS works, and is the source of its power. Because the link between features and attributes is dynamic, changing an attribute in the table automatically results in a change in the map. Themes: Desktop GIS links sets of features and their attributes and manages them together in units called themes. A theme contains a set of related features such as roads, or parcels, or waterways, which have a set of common attributes, for example commodity field sites would be grouped into a theme because they all represent parcels on which there is the potential for growing a commodity. Spatial Data: Perhaps the most important concept to consider when using GIS is the quality of the spatial and tabular data that is used. Provided the user understands the limitations of the data being used, and conveys this information in the map interpretation, then most data is of some value. All data used in a GIS should have metadata, which is usually a text document identifying the data source, the scale at which the data was created, the projection/coordinate system units, a listing of the attributes, etc. Referencing Spatial Data--Understanding Map Projections The locations of map features are referenced to actual locations of objects that they represent in the real world. The positions of objects on the earth's surface are measured in degrees of latitude and longitude, and are referred to as geographic coordinates. Geographic coordinates may be expressed in units of degrees minutes, and seconds (e.g. -120deg, 30 min, and 0 sec) or as decimal degrees (e.g. -120.5000). On a flat map, the locations of map features are measured in a two-dimensional planar coordinate system. These coordinates describe the distance from an origin (0,0) along the X and Y axes. Because the earth is round and maps are flat, getting the information from the earth's surface to a flat map requires the use of a mathematical formula called a map projection. This process of "flattening" can result in distortions of both distance and area, depending on the type of mathematical projection used. On large scale maps, such as street maps, the distortion caused by the map projection being used may be negligible because the map will typically cover only a small part of the Earth's surface. On smaller scale maps, such as regional and world maps, where a small distance on the map may represent a considerable distance on the Earth, this distortion may have a bigger impact, especially if your application involves comparison of the shape, area or distance of different features. In these cases, knowledge of the characteristics of the map projection you are using becomes more important. In California, which covers more area in a N-S direction versus an E-W direction, the Albers Equal Area projection allows the whole state to be included in just one zone, compared to UTM which divides California into two zones along the -120th parallel, and the state plane coordinate system which divides the state into 6 or 7 zones in a N-S direction. For this reason, the Teale Data Center and DPR, maintain all their spatial data in the Albers Equal Area projection. Many of California's counties, however, use the State Plane coordinate system because the zones of this system are oriented along county boundaries and this projection offers minimal distortion over these smaller county-sized areas. All the data sources represented on a particular view should be in the same map projection. Data sources of different map projections will not overlay correctly. Map Scale and Accuracy Detail--Determining What is Important: It is natural to equate detail with accuracy. However, when we talk about the level of detail on a map, we are referring to the quantity of geographic information shown. Map accuracy, on the other hand, is a statement of the quality of this information. On smaller scale maps there is simply not enough room to show all the available detail, so features such as streams and roads often have to be represented as single lines, and area features like cities, have to be shown as points. This is called generalization. When features are generalized their level of detail is reduced to avoid cluttering the map, but their overall shape and position is retained. It is important to consider the amount of detail that a specific project requires. For example, field sites represented as points don't give any information about their shape, and it is not possible to measure their dimensions or locate features, such as waterways, contained within them. On the other hand, points are probably the best way to best represent apiaries, since it is not important to know the shape of the bee hives. Scale--Understanding Why Different Datasets Don't Match Up: Some projects require a higher degree of locational accuracy than others. For example, if a feature representing a road or parcel boundary is mapped to within 40 feet of it's real world location, it may not be accurate enough for an engineering application or legal parcel assessment, but it may be perfectly adequate for a CAC wishing to identify the location of a commodity or pesticide use. It is important to note that while spatial data of all map scales (e.g. 1:1,000,000 to 1:1200) can be displayed in the same view by a GIS, their relative positions with respect to one another will vary greatly due to their accuracy. For spatial data generated at 1:24,000 (e.g. a USGS 7.5' Quad sheet) 1 inch represents 2000ft, whereas for data at a scale of 1:250,000, 1 inch represents approximately 4 miles. While data at these scales (1:250,000) may be useful, particularly if no other spatial data is available, it is important to bear in mind the relative accuracy of the mapped features compared to their actual locations on the ground. This is especially important to consider when the information is used to make judgments concerning distances of less than 1000 ft. In many instances, counties which have well established GIS programs in their planning or public works departments have often developed data layers at a scale of 1:4800 or better where 1 inch represents 400 ft (a ground accuracy of +/- 10ft). This spatial data provides GIS users with greater accuracy, giving them the potential for making better locational decisions. Large Scale Maps A large scale map is one in which a given part of the Earth is represented by a large area on the map. Large scale maps generally show more detail than small scale maps because at a large scale there is more space on the map in which to show features. Large scale maps are typically used to show site plans, local areas, neighborhoods, towns and cities. 1:2,500 is an example of a large scale. Small Scale Maps A small scale map is one in which a given part of the Earth is represented by a small area on the map. Small scale maps generally show less detail than large scale maps, but cover large parts of the Earth. Maps with regional, national, and international extents typically have small scales, such as 1:1,000,000. Note: When you zoom in on a view in ArcView, the scale of the view gets larger, and when you zoom out the scale gets smaller. Map Accuracy The accuracy of a map is not dependent on the map's scale. Map accuracy depends on: the accuracy of the original data used to compile the map, how accurately this source data has been transferred onto the map, and the resolution at which the map is printed or displayed. The accuracy of the maps you create with ArcView depends primarily on the quality of the coordinate data in your spatial database. To create the spatial data, existing maps or manuscripts may have been digitized or scanned, and other original data, such as survey reports, aerial photographs and images, and data from third parties may also have been used. The final map will therefore reflect the accuracy of these original sources. It is always important to consider map accuracy to ensure that your data is used appropriately. Don't base important decisions on geographic data for which you don't know the source and accuracy! How to Create Good Spatial Data: A desktop GIS allows users to create spatial data by drawing shapes over the top of existing maps or images. As an example, several CACs, including Fresno and Kern, have almost completed this task for their crop parcel layers using a combination of pre-existing assessor parcel data, street centerline data and aerial imagery as the base data layers. While existing parcel lines and street centerlines offer a tremendous head start, imagery also supplies many important details such as field boundaries, water features, etc., that may be absent from many data layers. Overview of Data You Can Use in ArcView Data that describes any part of the Earth's surface or the features found on it can be called geographic data. Geographic data from a variety of sources can be used in ArcView: Spatial data Spatial data is at the heart of every ArcView application. Spatial data is geographic data that stores the geometric location of particular features, along with attribute information describing what these features represent. Also known as digital map or digital cartographic data. The data you can use include: ArcView shapefiles ARC/INFO coverages Data layers in ARC/INFO Map Libraries CAD drawings (if ArcView's CAD Reader extension is loaded) Data managed by ESRI's Spatial Database Engine (SDE) (if ArcView's Database Themes extension is loaded) Image data - includes satellite images, air photographs and other remotely sensed or scanned data. The data you can use include: TIFF ERDAS .lan and .gis files BSQ, BIL, and BIP Sun rasterfiles Run-length compressed files ARC/INFO GRID data (displaying a grid as an image doesn't require ArcView's Spatial Analyst extension) JPEG (if ArcView's JPEG Image extension is loaded) Tabular data Tabular data can include almost any data set, whether or not it contains geographic data. What you can do with a table in ArcView depends on what it contains. Some tables can be displayed on a view directly, others provide additional attributes that can be joined to your existing spatial data. ArcView supports these formats: Data from database servers such as Oracle, Ingres, Sybase, Informix, etc. dBASE III files, dBASE IV files INFO tables Text files with fields separated by tabs or commas Hot Linking to Other Data Sources Using ArcView's Hot Link facility you can access virtually any other data source or application, simply by clicking on a view. For example, you might click on a building to display its floor plan, access a document describing it, or even play a video showing it. In this way ArcView lets you organize and access diverse sources of data geographically. ArcView's User Interface In ArcView you work with views, tables, layouts, charts and scripts stored in one file called a project. You work with one project at a time in ArcView. Projects enable you to keep all the components together that you need for a specific task or application. The Project Window When you create a new project or open an existing one, a Project window will appear in the ArcView window. The Project window lists all the components of the project and enables you to manage them. Double-click a component's name to open it. The title bar of the Project window shows you the name of the project. View, Table, Chart, Layout, and Script Windows When you open one of the components of a project, it is displayed inside its own window. You can have any number of windows open in ArcView, but at any time there is only one active window. The active window is the window you are currently working with. All the windows that are currently open inside the ArcView window are listed at the bottom of the Window menu in the ArcView menu bar. The first window in this list is the Project window. To make a window active, simply click inside it or on its title bar, or choose it from the list in the Window pulldown menu at the top of the ArcView window. When you open a window it automatically becomes active. If part of a window is hidden by others, making it active will bring it to the top. When you perform an action in ArcView, it usually applies to the active window. ArcView's user interface changes according to what is in the active window. So for example, when the Project window is active, you will see the buttons, tools and menus for working with projects. Menu bar This bar along the top of the ArcView window contains ArcView's pulldown menus. To choose a menu choice from a pulldown menu, you can use the mouse or a keyboard shortcut. Some keyboard shortcuts are listed in the menus. The availability of some menus depend on the graphical user interface (GUI) system you are working with. The contents of the menu bar change according to what is in the active window. Button bar This bar located beneath the Menu bar in the ArcView window contains buttons giving you quick access to various controls. Click on a button to choose it. The contents of the button bar change according to what is in the active window. Tool bar This bar located beneath the Button bar in the ArcView window contains various tools you can work with. If you are working on the Project window or on a script, there is no tool bar. You click on a tool to choose it. This may change the cursor to reflect the tool you have chosen. The chosen tool remains selected until you choose another one. The contents of the tool bar change according to what is in the active window. The Table of Contents Each view has a Table of Contents that lists the themes in the view and shows what symbols and colors they are drawn with. You also use the Table of Contents to control the order in which themes are drawn in the view. Creating and Using Maps What is a view? A view is an interactive map that lets you display, explore, query and analyze geographic data in ArcView. Views are saved in the ArcView project you are currently working with. A view defines the geographic data that will be used and how it will be displayed, but it doesn't contain the geographic data files themselves. Instead, a view references these source data files. This means that a view is dynamic, because it reflects the current status of the source data. If the source data changes, a view that uses this data will automatically reflect the change the next time the view is drawn. It also means that the same data can be displayed on more than one view. A view is a collection of themes. A theme represents a distinct set of geographic features in a particular geographic data source. For example, a view showing a country might have one theme representing cities, one theme representing roads, one representing rivers, etc. A view's themes are listed in its Table of Contents. What is a theme? A theme is a set of geographic features in a view. A theme represents a source of geographic data. E.g.: ARC/INFO coverage ArcView shapefile CAD drawing Image data source such as a satellite photo A table containing XY coordinates Street addresses that can be geocoded in ArcView Events that can be matched to route features Data can be on a local disk or accessed across a network. A theme points to the geographic data it represents. It does not contain the data itself. The themes in a view are listed in its Table of Contents. Each theme has its own legend displayed in the Table of Contents. A theme's legend controls how the theme is displayed on the view. Working with Tabular Data What is a table? A table lets you work with data from a tabular data source in ArcView. You can bring data from almost any tabular data source in your organization into ArcView as tables. Then you can add data from these tables to maps, and symbolize, query and analyze this data geographically.\ An ArcView table references the tabular data source it represents, but doesn't contain the tabular data itself. This means that tables are dynamic, because they reflect the current status of the source data they are based on. If the source data changes, a table based on this data will automatically reflect the change the next time you open the project containing this table. You can also choose Refresh from the Table menu to refresh the table at any time to see the current state of your source data. The definition of tables you add to ArcView are saved in the project file you are currently working on. New tables can be created in ArcView and some tables can be edited, depending on the type of tabular data source they represent and whether you have write permission to them. Sources of Tabular Data dBASE, INFO, and delimited text files You can add dBASE, INFO, and tab or comma delimited text files into ArcView as tables. These data sources can contain any data that you wish to work with in ArcView. For example, these tables might contain additional information about the features displayed on a view. SQL database servers From ArcView, you can connect to a database server, such as Oracle or Sybase, and run an SQL query to retrieve records from it as a table. ArcView stores the definition of the SQL query you used, not the records themselves. Attribute Tables of Spatial Data In addition to tables that are based on tabular data sources, some spatial data sources, such as shapefiles and ARC/INFO coverages have their own attribute tables containing descriptive information about the geographic features they contain. When you add a theme representing one of these spatial data sources to a view, you can access this attribute table by pressing the Open Theme Table button. ArcView automatically manages the relationship between themes and their attribute tables, so you don't need to load these tables into ArcView separately. When you open a theme's attribute table, you can select features on the view by selecting their records in the table, and vice versa. Joining tables You can join a table to the active table based on the values of a common field found in both tables. A Join establishes a one-to-one or many-to-one relationship between the destination table (the active table) and the source table (the table you are joining into the active table). Typically, the source table contains descriptive attributes of features that you wish to join into a theme's table so that you can symbolize, label, query and analyze the features in the theme using the data from your source table. Choosing a common field for the join--Tables are joined based on a field that is found in both tables. The name of the field does not have to be the same in both tables, but the data type has to be the same. You can join numbers to numbers, strings to strings, booleans to booleans and dates to dates. Any field can be chosen as the basis for a join, not just ones that uniquely identify geographic features. Fields storing attributes like parcel owner name, vegetation type, building materials, population size, etc. can be used too. For example, you might have a source table containing detailed information about different types of vegetation, and a theme table with a vegetation type field. You could join the tables together based on vegetation type so that the detailed information about the vegetation can be displayed on the view. Editing joined data--When editing a joined table, you can only edit the fields in the destination table. Edits to the fields from source tables must be performed directly on those tables. You can then use Refresh from the Table menu to show the changes in the joined table. How are joins saved?--When you save a project containing a join, ArcView saves the definition of the join rather than saving the joined data itself. The next time you open the project, ArcView rejoins any joined tables by reading their files from disk or re-executing the SQL queries they are based on. In this way, any changes to the source or destination tables that have taken place since they were last joined are automatically included in the project, and reflected in any views, tables, charts or layouts based on the joined data. Because joining tables has no effect on their physical files on disk, you don't need to have write permission to files to be able to join them in ArcView. For example, if you are working with themes representing geographic data accessed across your network from a remote, read-only GIS database, you can still join your own data tables to these themes and work with your data spatially. If you want to make a new table on disk to permanently store the joined data, you choose Export from the Table menu. You would do this, for example, if you wanted to use the table in another application. Linking tables A Link establishes a one-to-many relationship between the destination table (the active table) and the source table (the table you are linking to the active table). One record in the destination table is related to one or more records in the source table. Typically, the source table contains descriptive attributes of features that you wish to link to the features in a theme's table so that you can select features from this theme on a view see which linked records in the source table are selected. Unlike joining tables, linking tables simply defines a relationship between two tables, rather than appending the fields of the source table to those in the destination. When tables are linked, neither table is changed--they are just linked to one another. After a Link is performed, selecting a record in the destination table will automatically select the record or records related to it in the source table. An example of a one-to-many relationship is pesticide use. One field site have multiple pesticide applications. The table that is active when you choose Link is the destination table. The last table that was active is the source table. Choosing a common field for the link--Tables are linked based on a field that is found in both tables. The name of the field does not have to be the same in both tables, but the data type has to be the same. You can link numbers to numbers, strings to strings, booleans to booleans and dates to dates. Laying out and printing Maps What is a layout? A layout is a map that lets you display views, charts, tables, imported graphics, and graphic primitives. The layout is used to prepare these graphics for output from ArcView. A layout defines what data will be used for output and how they will be displayed. A layout can be dynamic because it allows you to make specific graphics live. When a graphic is live, it reflects the current status of the data. For example, if the data in a view changes, the layout automatically reflects the change. The same data can be displayed on a number of different layouts. What a layout can contain: The Layout provides the standard graphics and operations one would expect in a typical 'drawing' package. The graphics are drawn using the Draw tools and include points, lines, polygons, rectangles, and circles. The Layout also contains objects specific to the ArcView environment, including frames containing ArcView views, charts, and tables, and ancillary objects such as legends and scale bars. Printing Layouts You can print a layout or export a layout to a number of formats to use with other software packages. Customizing ArcView You can customize ArcView's menus, button bars, tool bars and popup menus so they contain the controls you use most often and remove those that you don't need. In addition, you can add scripts that you regularly use. These scripts can be associated with controls or events like opening or closing a document, or you can simply include them as part of your default settings. You can also customize the project window. To customize ArcView for your own use, you can create default settings for each default type (View, Table, Chart, Layout, Script, Project, Appl) and also create new user interfaces. ArcView reads your customized settings every time you start the application. Your defaults override the system defaults. ArcView's default settings are stored in a special project called default.apr in the installation directory or folder named 'etc'. Your personal default settings are stored in a special project, also called default.apr, located in your HOME directory. Extensions Extensions are add-on programs that provide advanced GIS functionality. When you load an extension ArcView's user interface changes to reflect the functionality in the extension. New menus, menu items, buttons and tools may appear, and new options may be available in existing dialogs. You load and unload extensions using the new Extensions dialog. This dialog is accessed by choosing the new Extensions option from the File menu when the Project window is active. You can load and unload extensions at any time during an ArcView session. You can load different extensions for different projects or make your choice of extensions the default for ArcView. If you open a project that uses an extension that is not currently loaded, ArcView will automatically load the extension for you. A number of supported and unsupported extensions are included with ArcView Version 3.x. In addition, extensions developed by third parties may be available.