Some basic tips on using CHGIS datasets are provided for various applications listed above. These are not meant to be tutorials on how to use the software, but are provided for a quick start. For more in-depth lessons on GIS skills, we recommend the folllowing websites:
What is GIS and how does it work? Please see the GIS Self-Learning Tool Web-based Tutorial.
How can I learn more advanced techniques? A virtual course is the Complete GIS Curriculum by the National Center for Geographic Information and Analysis
The CHGIS datasets can be roughly divided into two types of data:
- time slice data
- time series data
Time Slice Data refers to GIS layers that contain spatial objects representing a single year, or "slice in time." All of the 1820 and 1911 layers fall into this category. When working with time slice data, all of the spatial objects are represented as the documentation indicates they existed for a particular year. Therefore two adjacent areas, such as two prefectures, would share a boundary, and by means of visual exploration of the data it is easy to distinguish one from the other.
Time Series Data refers to GIS layers that contain many instances of spatial objects as they changed over time. Therefore, when spatial changes occurred to an object, both the previous and subsequent objects are included. Visually, this results in many overlapping objects, or "spaghetti," as it is referred to in GIS terms. Taking the two adjacent prefectures mentioned above, let us presume that from Time 1 to Time 2 a certain boundary was valid. But at Time 3 a boundary change occured. Because the boundary is shared by both the adjacent areas, it means that new objects are created for both areas. Therefore, instead of two objects we would have four objects. The changed portion of the boundary would show up as a distinct line, while the unchanged portion of the boundary would overlap the previous version.
When dealing with Time Series Data it is necessary to keep in mind the visual ambiguity of the temporally distinct spatial objects, or "historical instances," which are all stored in a single GIS layer. It is necessary to do a selection of the objects by a particular year, in order to see the equivalent of a Time Slice. Please see more details on using time series data.