This book provides relevant information about the sources and quality of available public domain spatial data. It can help guide you with finding, evaluating, and analyzing data to solve location-based problems. It also covers practical issues such as copyrights, cloud computing, online data portals, volunteered geographic information, and international data.
Allow enough time to find your data.
It might take several hours or even a few days to find the data you need.
The data you need may be within a larger dataset that covers many topics.
For example, data on glaciers may be in a land cover dataset.
Check for use restrictions.
Always look at the license or use restrictions for the data. Some will be free to use for educational or research purposes, but not for commercial uses. Always check citation requirements, too.
Datasets might not be GIS-ready.
The information you are seeking may be in tables or reports. You may need to put the data into a format that can be read by GIS software (such as by adding columns for latitude and longitude coordinates).
Always download the data's documentation.
The documentation or metadata will have essential information you will need to make sense of the data.
Always make note of where you downloaded the data sets from, as you go (it is easy to lose track!), and keep your downloaded data organized.
Five factors you should consider when deciding whether or not spatial data are suitable for your use include:
Positional/Spatial Accuracy: How close are the locations of the objects to their corresponding true locations in the real world? At what scale was the data created? Will this be sufficient for your needs.
Check the Attribute Table: Does the data set include the information you need? Can you interpret the values in the attribute table? Is there a metadata file to describe the attributes?
Logical Consistency: If you used this dataset with other datasets, will its spatial characteristics and attributes cause strange juxtapositions or illogical associations, such as a road that is also a canal? Does every area have a label point? Is the dataset consistent with its definitions? Does the data set's creation date correspond with your project? How does it correspond with other data sets you are using?
Completeness: Does your proposed dataset completely capture all of the features you need?
Provenance/Lineage: Does the dataset include metadata? Does the provenance or lineage of the data, i.e. who created it, how the data were created, meet your needs?
Adapted from Kerski, J.J., & Clark, J. (2012). The GIS guide to public domain data. Redlands, CA: Esri Press.
It is important not only to check the metadata of datasets before you re-use them, but also when you create new maps and/or datasets be sure to include complete and accurate metadata.
The Federal Geographic Data Committee (FGDC) developed the Content Standard for Digital Geospatial Metadata (CSDGM), which recommends certain items be included in geospatial metadata. The following are a summary of these areas. For more details on this and other metadata recommendations visit the FGDC's Geospatial Metadata Standards and Guidelines webpage.
Key Elements to Include in Metadata:
Identification: Name(s) of creator of data; publication date; title of the data; time period for data contents; frequency with which the data is maintained and updated; keywords associated with the data; bounding coordinates; background information about person and/or organization who created/collected the data.
Data Quality: Description of how data collected and/or if included data from other sources, then should include metadata on that.
Spatial Reference Information: If using map projection, its name and parameters; scale; if using a grid coordinate system, the grid name and parameters; horizontal datum.
Attribute Table Information: Field names and any aliases; type of data in each field; any relationships between the fields.
Use Restrictions: Outline of how the data can be used and distributed; how to cite it; contact information for any questions about re-use.