Geodatabases and Spatial Data
Geodatabase
A geodatabase is a data storage and management framework for ArcGIS. It stores spatial data within which rules and relationships to such data can be applied. Geodatabases maintain integrity of the spatial data with a consistent and accurate database. There are 2 types of geodatabase; single-user and multi-user geodatabases A single-user geodatabase is for individual GIS work in a desktop while a multi-user database is for large organizations that have a central, scale-able data storage and management system, it requires an ArcSDE technology which would hold the database.
Topology
Topology in GIS is a set of rules and behaviors that model how points , lines and polygons share coincident geometry, for example a set of county polygons within each state must completely cover the state and share edges with the state boundary. Topological rules are commonly used to manage coincident geometry in a geodatabase, it is important in ensuring data quality of spatial relationships and it also aids in data compilation. Some of the geodatabase rules can be seen in the image below.
Geodatabase topology rules(click to enlarge)
Creating a File Geodatabase and Validating Relationships using Topology Rules
Structure of File Geodatabase Created
Using the George Washington National Monument shapefiles data provided by the instructor, I created a file geodatabase called ‘GEWA’ with 4 feature dataset. I had a Biota feature data set with 2 feature classes (natural and Cultural vegetation); Inland Water Dataset with 2 feature classes (Streams and Water Bodies); Structure_ transportation with 3 feature classes (buildings, fences and roads) and the last dataset was named planning_features with 2 feature classes (boundary and small scale features). An image of the dataset created is shown below;
File geodatabase structure (click to enlarge)
Topological rules
Two topological rules were set; one in the Sturcture_transportation dataset and the second was in planning_features dataset.
The first created topology rule was in the ‘Planning_features” dataset. The feature classes in this dataset were the boundaries and small scale features and I chose to use the coverage(must be covered by) topology rule; where small scale features must be covered by boundary. I chose this rule so it is easy to see or validate the small scale features that fall into the GEWA NM boundary.
The second topology rule created was in the Sturcture_transportation dataset. I choose the “must not overlap with’ topological relationship between buildings and roads. I chose this as this should not be so in a real world example, one cannot have a road overlapping a building. This would check to make sure the map does not have such errors.
For the planning features topology, for small scale features that are within the park boundary, I had 1 topology error. There was one small scale feature which was outside of the boundary. Using the identify tool in ArcMap, I found out that this small scale feature was the ‘park entrance sign’. I guess this is a logical error since this sign would be located like a few feet or meter from the main park. I corrected this topological error by marking it as an exception.For the Sturcture_transportation building, I had one topological error, where a building (log house) was overlapping roads. I looked at the roads and building feature class closely, to see what could be responsible for them overlapping, it looked like a digitizing error and I also fixed this error by adding it as an exception
A map showing the datasets in the file geodatabase created and the and the validated topological relationships in the dataset was created. The final map is shown below.
map showing the GEWA datasets(click to enlarge)