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What Is Georeferencing?
a lot of headaches later on by using a common basis for the various geospatial
datasets you use. This is especially critical when getting several types of data
to accurately match up with one another.
However, a problem’s going to arise when one (or more) of your pieces
of data doesn’t have coordinates assigned to it, or you don’t have any information as to what projection or datum was used to construct it. Think about
this—you obtain an old map of your town, scan it into a computer, and want
to add it to other layers (like a road network or parcel layer) in a GIS to see
how things have changed since that old map was made. You add the layers
into the GIS, but the scanned historic map won’t match up with any of your
data. This is because that image doesn’t contain any spatial reference (such
as a real-world coordinate system). Although it might show features like old
roads or the dimensions of a building, the only coordinate system the old
map possesses is a grid that begins at a zero point at the lower left-hand
corner and extends to the dimensions of the scanned image. For instance,
coordinates would be referenced by whatever units you’re measuring with
(such as 200 millimeters over from the left-hand corner and 40 millimeters
up from the left-hand corner).
Items in the image can’t be referenced by something like latitude and longitude since those types of coordinates haven’t been assigned to anything in
the image. Similarly, when you added this scanned image as a layer in a GIS,
the software wouldn’t know what to do with it when trying to match it up with
other data layers (which have referenced coordinate systems). Without knowing “where” your scanned image matches up with the rest of the data, you’d
be unable to use this image as geospatial data (or reproject it to match your
other data). The same concept holds for other types of data used with geospatial technology. That is, if they all automatically had the correct spatial reference when they were created, things would be a lot easier. So what you’ll have
to do is match the data to the map, or assign a real-world set of coordinates to
your data so it can synch up with other geospatial data. In other words, you’re
going to have to georeference your data.
What Is Georeferencing?
Georeferencing is the process of aligning an unreferenced dataset with one
that has spatial reference information. Other terms used for similar types of
processes include “image to map rectification,” “geometric transformation,” or
“registration.” For example, say you’re hosting a meeting at your school and
want to make a map for the invitation to direct people not only to the school,
but also to your specific building within the campus. You go to your school’s
Website and download a map that shows the campus boundaries and specific
building locations on the campus. So far so good, but you want to place that
downloaded map in the greater context of a map of the city in a software program to show where your campus building is in relation to the surrounding
spatial reference the
use of a real-world
coordinate system for
identifying locations.
georeferencing a
process whereby
spatial referencing
is given to data
without it.
What Is Georeferencing?
a lot of headaches later on by using a common basis for the various geospatial
datasets you use. This is especially critical when getting several types of data
to accurately match up with one another.
However, a problem’s going to arise when one (or more) of your pieces
of data doesn’t have coordinates assigned to it, or you don’t have any information as to what projection or datum was used to construct it. Think about
this—you obtain an old map of your town, scan it into a computer, and want
to add it to other layers (like a road network or parcel layer) in a GIS to see
how things have changed since that old map was made. You add the layers
into the GIS, but the scanned historic map won’t match up with any of your
data. This is because that image doesn’t contain any spatial reference (such
as a real-world coordinate system). Although it might show features like old
roads or the dimensions of a building, the only coordinate system the old
map possesses is a grid that begins at a zero point at the lower left-hand
corner and extends to the dimensions of the scanned image. For instance,
coordinates would be referenced by whatever units you’re measuring with
(such as 200 millimeters over from the left-hand corner and 40 millimeters
up from the left-hand corner).
Items in the image can’t be referenced by something like latitude and longitude since those types of coordinates haven’t been assigned to anything in
the image. Similarly, when you added this scanned image as a layer in a GIS,
the software wouldn’t know what to do with it when trying to match it up with
other data layers (which have referenced coordinate systems). Without knowing “where” your scanned image matches up with the rest of the data, you’d
be unable to use this image as geospatial data (or reproject it to match your
other data). The same concept holds for other types of data used with geospatial technology. That is, if they all automatically had the correct spatial reference when they were created, things would be a lot easier. So what you’ll have
to do is match the data to the map, or assign a real-world set of coordinates to
your data so it can synch up with other geospatial data. In other words, you’re
going to have to georeference your data.
What Is Georeferencing?
Georeferencing is the process of aligning an unreferenced dataset with one
that has spatial reference information. Other terms used for similar types of
processes include “image to map rectification,” “geometric transformation,” or
“registration.” For example, say you’re hosting a meeting at your school and
want to make a map for the invitation to direct people not only to the school,
but also to your specific building within the campus. You go to your school’s
Website and download a map that shows the campus boundaries and specific
building locations on the campus. So far so good, but you want to place that
downloaded map in the greater context of a map of the city in a software program to show where your campus building is in relation to the surrounding
spatial reference the
use of a real-world
coordinate system for
identifying locations.
georeferencing a
process whereby
spatial referencing
is given to data
without it.