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GIS Web Application FAQ's
Please click on a link below to find answers to commonly asked questions about the online interactive mapping tools that are available for the Public and Prince William County staff. Additional questions can be directed to the Prince William County GIS Division by e-mailing
County Mapper XM

Why did the old version of County Mapper go away?
Because the underlying technology used to build the previous online mapping system has gone through significant changes and improvements, the computer hardware and software used to provide the previous version is no longer be available or supported by our software vendor.

How much longer will the old version still be available to use?
The previous release of County Mapper will be available to use until January 1, 2011.

Why do I have to print through the printer icon? Why can’t I just go to File>Print?
Because the image that you are viewing from the initial PWC Mapper window is actually referring a virtual image on the server, you must go through the printer icon to “capture” the image. Click on the printer icon to show the printing drop down box and select Print Preview. A new window will pop up and you will be taken to a Printing: Layout Page. If this page fails to appear, make sure that you have allowed for pop up from our site. From the Printing: Layout Page your map is now available for printing. If you do not go through the printer icon to get the layout page and you print directly from the PWC Mapper window, there will be missing data on your printed page.

Why can’t I control the zoom in and out at very small intervals?
To improve performance, data layers are “cached” for faster data retrieval. Caches are built at set scales and cannot be dynamic. When users zoom in or out, the zoom level will adjust to the closest cached scale. Scale caches are built at 1:300, 1:600, 1:1200, 1:2400, 1:4800, 1:9600, 1:19200, 1:38400, 1:76800, 1:153600, 1:307200 with a relative scale range of 20 feet to 4 miles.

Will I get the same results if I search by Premise Address versus Parcel Address?
No. Premise Address and Parcel Address searches are very different.  Links for Adjoiners/More Info/Tax Info are not available for premise address searches. These options are only available on parcel address or GPIN searches. That is because premise addresses are associate to a POINT rather than an AREA, which is the case with parcel. 
Parcel addresses are assigned to a single piece of land. Premise addresses are assigned to buildings and/or units that are located on parcel of land. In cases where the parcel of land contains a single structure that is owner-occupied, the parcel address and the premise address will be the same. In cases where many structures are located on the same parcel (e.g. apartments or business complexes), the premise address will be different than the parcel address.  It is recommended to always search by parcel address first and then search by premise address.

Why doesn’t the Identify button display results for parcels in a formatted layout like the old version of County Mapper?
Because County Mapper XM gives the user the ability to identify multiple layers, formatting must be generic to account for the variety of information displayed. The information displayed through the identify tool is displayed as it exists in the raw GIS data. This method allows for users to view all feature attributes. If a user wishes to view the details of a single property and have the ability to display extensive details about the property, it is recommended to use the Quick Search Function.

Why does the image not print out?
Because the image that you are viewing from the initial PWC Mapper window is actually referring a virtual image on the server, you must go through the printer icon to “capture” the image. Click on the printer icon to show the printing drop down box and select Print Preview. A new window will pop up and you will be taken to a Printing: Layout Page. If this page fails to appear, make sure that you have allowed for pop up from our site. From the Printing: Layout Page your map is now available for printing. If you do not go through the printer icon to get the layout page and you print directly from the PWC Mapper window, there will be missing data on your printed page

Why can’t I keep my saved settings under MyMap?
Saving extents and layers under MyMap requires that the user’s Internet browser accepts “cookies”.  If a cookie is removed, then the saved extent is also removed.  Failure to save extents are typically a result of when the Internet browser setting is turned off for accepting cookies or the user cleans out the temporary Internet files nightly.

Why can’t I get the measure tool to draw anything?
When using the measure tool, users should use a SINGLE click to start a line or change direction of a line and should use a DOUBLE click to end the line. If a user double clicks to start a line, the tool interprets that as the start and stop point being the same location and nothing will be drawn on the screen.

Why doesn’t my layer show up in the list when using Identify?
For a layer to show up in the Identify layer list, it must be turned on and visible. Go to the Layers tab and verify that the box is check. If not, check the box to turn the layer on, go back to the Identify dialog box and click Update List. The layer should now be shown in the list.

Do I have to enter a title when printing?
No, entering a title is optional. You are also not required to print Results or the Legend. However, if you wish to print the Results you must a feature selected and information displayed in the Results Tab, otherwise this check box will not be available to be selected. The Legend must be loaded for this option to be available. Since the legend is not loaded by default, users can load the legend by clicking on the Legend tab and click the Load Legend button. 

What happened to the Legend with all the symbols? Why can't I see it?
To increase performance, the legend is not loaded by default. A user has the option of turning the legend on by clicking on the Legend tab on the right side of the screen and clicking the Load Legend button. Once the legend is loaded, it becomes available for printing and will update dynamically as layers are turning on and off.

Why do I get boxes with a red X inside when printing my legend
When loading the legend in the Legend tab, a virtual link is created between your dynamic map layers and a temporary symbols file the server. This link remains active for approximately 10 minutes after which time it will timeout and lose the reference. When the reference is lost, users will see a white box with a red X displayed in place of the legend symbol on the print preview page. Once the reference is lost, users will have to completely exit the application and re-enter to reload the legend and re-establish those links. It is recommended to load the legend when users are ready to print the document rather than at the beginning of the mapping session.

How can I cut and paste the map into an e-mail or document?
The cut and paste functionality is not inherent to the County Mapper XM printing functionality. GIS is working to improve this, however, and currently a workaround can be used as follows:
1. Print map as PDF
2. Open PDF in viewer
3. In PDF viewer, select Tools>Select & Zoom> Snapshot Tool
4. Use snapshot tool to define area to copy (don’t forget the disclaimer!)
5. Snapshot tool automatically copies to clipboard
6. Go to e-mail or file document and select Paste.

How do I link to the Real Estate Assessments data?
Links to the Real Estate Assessments data are only available when searching a parcel. A link can be found when using the Identify tool on the parcel layer only. The Tax Info button that is shown in the Results tab when locating a parcel with Quick Search will also provide this information. When activating the link, a new window will pop up and users will be taken to the Land Rover application. Please ensure that pop up blockers are turned off to use this feature.

How do I find Adjoiner information for my property?
Adjoiner information is only available when searching for a Parcel using Quick Search. When selecting the Adjoiner button, links will appear in the Results tab that display the Owner and Address information of all properties that TOUCH the selected parcel. Users may hover their mouse of the word HIGHLIGHT to show which parcel the link belongs to on the map.

What does the More Info button do?
The More Info button does just that – provide more information about the selected property. It is only available when a parcel is searched using Quick Search. More Info displays school district information, voting district information, subdivision and environmental information, as well as links to other databases if available.

What are the dialog boxes so big and I must use the scroll bars for viewing?
County Mapper XM was designed to be displayed using the standard computer resolution of 1280x1024, therefore, that is the optimal resolution setting recommended. If a user has a smaller setting to display larger icons, the dialog boxes will be enlarged with scroll bars.

Why does the map react if I just simply click on it? I didn’t tell it to do anything.
When a user clicks on the map canvas (map image) and it does something unexpected, always check the Current Tool on the County Mapper XM toolbar to see which tool is active. Often times a user will unknowingly have the zoom tool active. To deactivate any tool and return control back to the mouse, click the red X located on the County Mapper XM toolbar next to the Pan tool.

Why do I see a blank document when I look at print preview in landscape?
Depending on the user’s personal printer settings and paper margins, some users may have to change their page size to 90% to allow for the entire image to print out.

How can I find the location of different data layers to turn them on and off?
Data layers are listed under the Layers Menu and are organized based on their business use. There are nine “tabs” or categories that are shown in the drop down menu. Each tab has a collection of layers associated with that category. Next to each layer name, a box can be checked to turn the layer’s visibility on or off.

How do I use the transparency tool bar?
The transparency tool bar controls the shading level of a layer on the map. The shading can be made heavier or lighter by sliding the transparency bar.  The transparency only controls all the layers within that tab but is independent from other tabs. For example, transparency levels can be made heavy for Land Development and very light for Environmental. This allows the user to customize the map appearance to their individual need.
Aerial imagery is always the base layer in which all other layers are overlaid. Think of it as the bottom piece of bread in a sandwich. It cannot be made transparent because there is nothing underneath the aerial imagery to view.
The red X is the deactivate button. It restores the selection tools back to the default settings and returns the control to the computer mouse.
The parcel history tree application is a tool that quickly displays the parent-child relationship for a GPIN. It is meant as a tool and guideline to assist in parcel research, however, it is not all inclusive prior to the year 2000 and does not provide lineage for properties created prior to 1994 when the GPIN numbers were first established.

Why can't I change the transparency on a shaded graphic that I just added with the redlining tool?
Users must set the transparency level prior to drawing the shaded graphic. Once the graphic has been drawn, the transparency level cannot be changed.

How do I unselect features or clear the highlights on a property?
There are two ways to clear the highlight. In the Results tab, click the Clear Results button or under Map Tools menu, select Clear Search Graphics.

How do I search for a subdivision?
Users can locate subdivisions by clicking on Quick Search and select the Features tab. In the drop down box under Select Layer, choose Subdivisions. Subdivision names can be selected through the Select Options drop down box or the user may begin typing in the subdivision name. The Select Options box will narrow the results as the user types the desired name.
Why do I need to copy the disclaimer when cutting and pasting images into e-mails and documents?
Prince William County asks that when using a PWC map, either paper or electronically, to present the image with the disclaimer attached to avoid confusion or misrepresentation and ensure that the recipient understands that it is for display purposes only and is not to be used or construed as a legal instrument.

Why does printing results with scroll give me problems? My results don’t fully print when I have multiple features selected. What’s with the scroll bar and where is my information?
This is a bug in the printing functionality with County Mapper XM. Prince William County GIS Developers are working to resolve the issue. There is no workaround at this time.

 question isn’t shown on the list. What do I do now?
If your question is not shown in the FAQs, please contact GIS staff at 703-792-6840 or e-mail with your comments or questions.


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