Geographic Information Systems FAQs
Geographic Information Systems (GIS)
What is a geographic information system (GIS)?
What kind of data is used in a GIS?
What is spatial data?
What is attribute data?
What is the value of linking spatial and attribute data?
How does Baltimore County use GIS?
What data is available to the public?
Public Access Questions
Where do I obtain GIS products and services?
What are the hours of operation?
What products are available for purchase?
What are the available data formats?
Where can I get more information about available data?
What services are available?
What are custom maps?
What are custom reports?
What is analytical analysis?
How is the data divided up into tiles?
How can I determine where my area of interest is according to the tiling structure?
How long does it take to complete an order?
Map Data
Why is my house not shown on the buildings layer?
How often will the buildings be updated?
Why is my house not on the photograph?
How often will the photograph be updated?
How do I report discrepancies in the data?
Geographic Information Systems
Q. What is a geographic information system (GIS)?
A. GIS is a tool that displays and analyzes map themes to obtain more information about a feature.
Q. What kind of data is used in a GIS?
A. GIS uses two types of data: spatial and attribute.
A. Simply put, spatial data is digital maps and photographs. The data has special properties that allow the data to be viewed and analyzed on a computer. Spatial data can be further defined as vector and raster. Vector data has features made up of points, lines and polygons. Raster data is made up of pixels (picture elements).
A. Attribute data is what we know about a feature. Examples of attributes include address, name, size, value, etc. Attributes are usually stored in databases or spreadsheets. In a GIS, attributes can be linked to spatial data.
Q. What is the value of linking spatial and attribute data?
A. Linking spatial and attribute data allows the user to analyze the relationships between the location of features and their attributes. For example, you can find all of the buildings within one mile of a location that are over 50,000 square feet in size.
Q. How does Baltimore County use GIS?
A. Baltimore County agencies use GIS for a variety of applications. GIS is used in Planning, Public Safety, Environmental Protection, Infrastructure Management and numerous other applications. For more information, follow the link to the GIS Strategic Business Plan.
Q. What data is available to the public?
A. Most GIS data produced by the county is available to the public. The only data that is not available is data with restricted access, such as protected by the Privacy Act.
Public Access Questions
Q. Where do I obtain GIS products and services?
A. GIS products and services are available in the Office of Information Technology, GIS Lab. The GIS lab is located in Room 46 of the Old Court House.
Q. What are the hours of operation?
A. The GIS Office is open Monday thru Friday, 8:30 am to 4:30 pm, except on holiday closings.
Q. What products are available for purchase?
A. Products include map data, attribute (descriptive information about map features) data and published maps. The County's base map data and most thematic data are available for purchase.
Q. What are the available data formats?
A. Map data is available in computer-aided drafting and design (CADD) export format (.dxf), shapefiles (.shp), and ArcGIS geodatabase (.gdb). Images are available in tag image format (.tif) and MrSID compression (.sid) formats.
Q. Where can I get more information about available data?
A. Data about the data, commonly referred to as metadata, is available from the Descriptions page. The Descriptions page has abstracts on each data layer listed (Federal Geographic Data committee (FGDC) compliant metadata).
Q. What services are available?
A. GIS services include production of custom maps, custom reports and analytical analysis. In addition to paying for the products involved in producing the custom product, $25 per hour is charged for developing a customized product.
A. Custom maps generally involve combining several map themes in a single product. An example would be to combine property lines with an orthophotograph.
A. Custom reports are generated from existing attribute databases. The requestor specifies the content and format.
Q. What is analytical analysis?
A. Analytical analysis involves performing spatial analysis to develop new information. An example would be overlaying zoning and parcel data to get an estimate of development potential.
Q. How is the data divided up into tiles?
A. The County uses two standard grids, 200 scale and 600 scale. The 200 scale grid is 6,000 feet by 4,000 feet. The 600 scale grid is 18,000 feet by 12,000 feet.
Q. How can I determine where my area of interest is according to the tiling structure?
A. The FindTile application is available to assist internet user's to locate the tiles in their area of interest. Walk-in customers can use index grids available in the GIS Lab.
Q. How long does it take to complete an order?
A. Orders are generally available 24 hours after the request is received. Customers with orders requiring additional time will be contacted in advance by phone or e-mail.
Map Data
Q. Why is my house not shown on the buildings layer?
A. The buildings layer is part of the County's planimetric/topographic database that was compiled from aerial photography dated 2005. Click on the aerial photography link for a graphic that shows a general overview of what areas where compiled when.
Q. How often will the buildings be updated?
A. The buildings will be updated periodically based on the database maintenance schedule. Refer to the Data Section under Resources for announcements of new data.
Q. Why is my house not on the photograph?
A. The photograph is from imagery acquired in the spring of 2008. Changes to the landscape after that date will not be on the photography.
Q. How often will the photograph be updated?
A. The photograph will be updated periodically. Refer to the Data Section under Resources for announcements of new data.
Q. How do I report discrepancies in the data?
A. Information about Data Discrepancies can be forwarded to the Office of Information Technology, Business Application Unit/GIS. Send comments to: gis@baltimorecountymd.gov.
