Interactive Mapping / How to Use the Viewers
How to Use the Viewers
Introduction to GIS Internet Mapping
Welcome to the exciting world of GIS Internet mapping! GIS Internet mapping is a powerful new system that combines visual geographic information-that is, maps-with the computer software to interpret and analyze that information, all served to your office or home via the Internet. Like traditional paper maps, GIS Internet maps provide us with images of our cities, counties, and states along with the usual geographic information like political boundaries, roads, or bodies of water. But instead of the what-you-see-is-what-you-get concept of the paper map, GIS Internet maps can store much more information about the map's features in a separate database, a database that can be accessed from any computer linked to the right Web site.
With a GIS map of Maryland, for example, you could point your cursor at the various Maryland counties, click your mouse button, and information about those counties--such as total area, population, etc.--would appear in a dialogue box on your computer screen. What's more, the different kinds of information available in a GIS map are stored in layers that can be turned on or off depending on your needs. If you were looking for parks to visit in Maryland, you could turn on the data layer that contains information about parks. If instead you are interested in power line corridors, you could turn off the parks layer and switch on the power line layer.
GIS maps also give you the power to define your searches for geographical information. Say you were looking for the most direct route to travel by car from one end of your county to the other. You would access a GIS map of your county via the Internet and switch on the roads layer. But suppose you then decided that you wanted the fastest route from one end of your county to the other. You could query the map's database to display only those roads that are four lanes wide or wider. You can even zoom in to get a closer look at a specific area on the map or pan across the map to find exactly what you are looking for!
The Internet Mapping Toolbox
The GIS maps supplied on this Web site are equipped with a set of tools designed to let you perform the functions of adding and removing map layers, querying map databases, panning, zooming, and other functions. Below you will find a description of the various mapping tools you will be using as you explore the maps on this Web site. After reading through these descriptions, you may want to link to our Mapping Toolbox Demo, which will guide you through the use of the various Internet Mapping Tools.
The Basics
When you open the window for a map on this Web site, the first thing you may want to do is become familiar with the geographical area the map covers. There are several tools you can use to navigate your map.
Zoom In-When you open your map window, the map will appear in its full extent, meaning that the map will depict the largest area of land possible. By clicking the Zoom In icon, you can move in on a selected area for a closer look. There are two ways you can use the Zoom In tool. First, after choosing the Zoom In tool, you may simply point your cursor and click on the area on your map you want zoom in on. Your computer will reload the map, changing the map extent to depict a smaller area of land centered where you have clicked. The second way you can use this tool is to drag a box around the area of land you wish to zoom in on by holding down on your mouse button and dragging the red box across the selected area. Again, the computer will reload the map. Repeat either of these procedures to zoom in yet closer.
Zoom Out-Use this tool in the same manner as the Zoom In tool to broaden your map extent.
Zoom to Full Extent-Use this tool whenever you wish to return your map to its fullest extent.
Zoom to Active Layer-Use this tool to zoom to the full extent of a specified data layer (see Add Layers below).
Pan-Click the Pan icon to move about on your map. Place the icon on your map and hold down your mouse button. Now drag the map to one side and let go of your mouse button. The computer will reload your map, centering it to its new location.
Pan One Direction-You may also pan across your map using the Pan arrow buttons. By clicking on one of these buttons, the computer will reload your map, re-centering it in the direction you have chosen.
Previous Extent-On some viewers you may be able to navigate from one extent to the next. Clicking Previous Extent will take you to the map view displayed previous to the one shown on your screen-a feature similar to the Forward and Back buttons on your Web browser.
Overview Map-Click this icon to display a smaller image of your map at its broadest extent. The overview map will highlight the area currently being viewed in the main map window.
The Next Step
Now that you've learned to move about on the map, you are ready to start using some of the tools that allow you to extract and analyze the information stored in your map's database. The following tools will help you find just the right kinds of information you will need for your geographical investigation. Also, the tools to print and copy maps, as well as save, open, and close projects will be described.
Add layers-As was described in the Introduction to GIS Internet Mapping, GIS map information is stored in individual data layers that can be turned on and off at the map user's request. When you open a map window, the layers you wish to work with may or may not be turned on. In order to turn on layers you want to work with, or turn off those you do not, you will use the Legend/Layer List button on your toolbar. Clicking the Legend/Layer List button once will bring up your map's legend, while clicking twice will bring up a list of the map's available layers.
For each available data layer, you have two choices: either to make that layer visible or to make that layer active. A visible layer is just that-the layer will be displayed on your map. An active layer is a layer that is not only displayed on your map but is also linked with its attribute database. In other words, an active layer is one whose attribute information is available to the map user and can be accessed using the Identify, Find, or Query tools.
Identify-This tool is used to retrieve attribute information for a feature on your map. In order to use this tool for a specific map feature, the data layer that contains that information must be made active (see Adding Layers, above). Once a layer has been made active and the Identify icon has been clicked, point your cursor on the feature you want to identify and click on it. If information for this feature is stored in the database, a box will appear listing the feature's attributes.
Find-Use the Find tool to locate specific features on your map. After pressing the Find icon, type the name or a description of the feature in the text box that appears. Specify the layer(s) you would like the computer to search. A list of feature options will be given below. Click on the feature or features you are interested in. The map will be reloaded, and the features you selected will be highlighted on the map.
Query-Use this tool to find all map features that fall within a specified range of values. For instance, suppose you were searching a map of Baltimore County in the hope of finding a suitable piece of land on which to build a new hardware store. Clicking on the Query button, you would choose the appropriate field to search; in this case you might choose "Land Available for Purchase." Then, under the Values box you might select the category "Zoning-Commercial," using the addition (+) sign to build the value of your query since you want a piece of land both available and zoned for commercial uses. Click Execute and a list of properties falling under those specifics will be given. You can then choose to highlight those properties on your map.
Measure-You can measure the distance between two or more points on your map by using the Measure tool. Suppose your map window was open to a map of the United States and you wanted to measure the distance between Detroit and Baltimore by way of Akron, Ohio. Click the Measure icon. Place your cursor on Detroit and click. Move your cursor to Akron and click again. At the top of your map, the total distance between these two points will be displayed. Now, click on Baltimore. The total distance for both segments will be displayed at the top of the screen as well as the distance for the segment between Akron and Baltimore.
Locating an Address-On some maps, you may be able to locate an address by typing it into the Locate Address dialogue box. First, click the Locate Address icon and type the address into the dialogue box. Click locate. The results will be listed in the panel below and a label will appear on your map. You may also instruct the computer to Pan To or Zoom To that point on your map.
Select Features-Use this tool to highlight specified features on your map and to retrieve attribute information on those features. First, activate the layer containing the data for the feature you want to select. Click the Select Features icon. You can then decide whether you want to select your map feature(s) by means of a line or polygon (a polygon is a series of lines that encloses a specific area-the simplest polygon is the triangle). Drag your line or polygon across the map area containing the features you want to select. All features in the activated layer(s) that come into contact with the line or polygon will be highlighted on your map. A box on the bottom of your screen will provide attribute information for the highlighted features.
Clear All Selections-Use this tool to clear those features selected using the Select Features tool.
Printing a Map-Click the Print icon. If prompted, type a map title and click Create Print Page. Otherwise, just click OK.
| 
