M@IN - Accessing Spatial Data Tutorial


Geographic Information and GIS - Data Access

Issues to Consider - Using Spatial Data

When looking for spatial data, the GIS user should consider the application and how the data will be used. Through this process, the user may want to address the following issues:

Data Requirements - What data layers or themes are required for the application?

Scale - Spatial data are typically derived from existing maps or aerial photographs. The scale of the source maps determines the scale of the data. Spatial data developed from a state or regional map may not be suitable for developing a map or doing analysis at a neighborhood level. In addition, data themes developed from different scale maps may not match up well.

File Size - How large are the files for the data themes that I need? Will my computer be able to efficiently manage and process the data?

Accuracy - Some applications may require great accuracy, others less so. How important is accuracy to your application?

Format - Data developed for a particular GIS software package is stored in a format or structure that is unique to that software package. If you are using a different GIS software package, it may not be able to read or understand that format. Will you be able to convert the data to the format you need?

Media - Spatial data suppliers typically provide data on some type of magnetic media - 1/2 inch cartridge, 3.5" diskette, 8mm tape, etc. What type of tape reader does your computer support?

Cost - Data are rarely free. Even government agencies typically charge a reproduction fee for providing data.

For some years now, numerous government agencies - at the federal, state, and local level - and other organizations have been developing spatial data. The dilemma for GIS users is posed by the following questions:

The NSDI is a national effort to link data users with data providers.

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