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Chapter 5 Working With Digital Spatial Data and GIS
After the join, information for the records from the Census information table is now associated with the corresponding records from the states’ table. For
instance, you could now select the record for Alaska and have access to all of its
housing information since the tables have been related to each other. In this way,
joining tables is a simple method for linking sets of data together and especially
for linking non-spatial spreadsheet data to spatial locations. With all of this other
data available (and linked to a spatial location), new maps can be made. For
instance, you could now create maps of the United States showing any of the
attributes (total number of houses, number of vacation homes, or percentage of
the total housing that are vacation homes) linked to the spatial features.
What Other Kind of Information
Do You Need to Use GIS Data?
Once you have your spatial and attribute data within the GIS, there’s one
more important piece of data you’re going to need—descriptive information
about your data. When creating data or obtaining it from another source, you
should have access to a separate file (usually a “readme” text file or an XML
document) that fully describes the dataset. Useful things to know would be
information about the coordinate system, projection, and datum of the data,
when the data was created, what sources were used to create it, how accurate
the data is, and what each one of the attributes represents. All of this kind of
information (and more) is going to be critical to understanding the data to
properly use it in GIS. For instance, if you have to reproject the data, you’re
going to have to know what projection it was originally in, or if you’re going
to be mapping certain attributes, then you’ll have to know what each one of
those strangely named fields in the attribute table actually represents. In GIS,
this “data about your data” is referred to as metadata.
The Federal Geographic Data Committee (FGDC) has developed some
standards for the content and format that metadata should have. These include:
a Identification of the dataset (a description of the data)
a Data quality (information about the accuracy of the data)
a Spatial data organization information (how the data is represented, such
as vector or raster)
a Spatial reference information (the coordinate system, datum, and
projection used)
a Entity and attribute information (what each of the attributes means)
a Distribution information (how you can obtain this data)
a Metadata reference information (how current the metadata is)
a Citation information (if you want to cite this data, how it should be done)
a Time period information (what date does the data represent)
a Contact information (whom to get in touch with for further information)
metadata descriptive
information about
geospatial data.
Chapter 5 Working With Digital Spatial Data and GIS
After the join, information for the records from the Census information table is now associated with the corresponding records from the states’ table. For
instance, you could now select the record for Alaska and have access to all of its
housing information since the tables have been related to each other. In this way,
joining tables is a simple method for linking sets of data together and especially
for linking non-spatial spreadsheet data to spatial locations. With all of this other
data available (and linked to a spatial location), new maps can be made. For
instance, you could now create maps of the United States showing any of the
attributes (total number of houses, number of vacation homes, or percentage of
the total housing that are vacation homes) linked to the spatial features.
What Other Kind of Information
Do You Need to Use GIS Data?
Once you have your spatial and attribute data within the GIS, there’s one
more important piece of data you’re going to need—descriptive information
about your data. When creating data or obtaining it from another source, you
should have access to a separate file (usually a “readme” text file or an XML
document) that fully describes the dataset. Useful things to know would be
information about the coordinate system, projection, and datum of the data,
when the data was created, what sources were used to create it, how accurate
the data is, and what each one of the attributes represents. All of this kind of
information (and more) is going to be critical to understanding the data to
properly use it in GIS. For instance, if you have to reproject the data, you’re
going to have to know what projection it was originally in, or if you’re going
to be mapping certain attributes, then you’ll have to know what each one of
those strangely named fields in the attribute table actually represents. In GIS,
this “data about your data” is referred to as metadata.
The Federal Geographic Data Committee (FGDC) has developed some
standards for the content and format that metadata should have. These include:
a Identification of the dataset (a description of the data)
a Data quality (information about the accuracy of the data)
a Spatial data organization information (how the data is represented, such
as vector or raster)
a Spatial reference information (the coordinate system, datum, and
projection used)
a Entity and attribute information (what each of the attributes means)
a Distribution information (how you can obtain this data)
a Metadata reference information (how current the metadata is)
a Citation information (if you want to cite this data, how it should be done)
a Time period information (what date does the data represent)
a Contact information (whom to get in touch with for further information)
metadata descriptive
information about
geospatial data.