Using an Observations Data Model in a GIS Framework
Tyler Jantzen, CRWR
July, 2006
Table of Contents
-
Create the appropriate Relates between the tables and shape files
-
Determine variables measured at the mouth of the Nueces River
-
Find all Values for a particular site, and select a single Variable
Introduction
Hydrologic Information System
The need to make hydrologic information more widely available has long been recognized as a priority among the hydrologic research community. National datasets combined with regional and local observatory datasets offer the potential to investigate hydrologic science in more depth than ever before. However, not all sources of hydrologic data are readily available. These sources are often stored in incompatible formats such that significant difficulty exists in merging these datasets into a common table or database. One method of dissemination of hydrologic data is a Hydrologic Information System (HIS). A HIS is currently being developed at National scale through the efforts of the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI)[1]. Similar efforts are being conducted at regional scales to make regional and local data available. While an “enterprise” HIS can be created at larger scales, similar “workgroup” HIS can be developed within a research group to share data in a consistent format. The following exercises and tutorials provide hands-on examples of how to use this data in a GIS framework.
Figure 1: The Concept of a Hydrologic Information System
Observations Data Model
The goal of a HIS is to make comprehensive hydrologic information from multiple scales available in a format that is easy to use. The Observations Data Model (ODM) has been developed as a universal data structure in which to store observations data, and has greatly assisted the creation of a HIS. At the time of publication for this tutorial, the ODM had been developed through version 3.0. See the accompanying document “CUAHSI Community Observations Data Model Working Design Specifications Document- Version 3” by Tarboton, Horsburgh, Maidment and Jennings for a more in depth description of this model and its specifications.
Figure 2: Observations Data Model v. 3.0 Schema[2]- a universal data structure
The strength of the ODM is derived from the fact that a single database structure can be used for various sources of data. Because this data is stored within the same structure, data from multiple sources can be merged and treated as a single source. An investigator can now look at different datasets describing similar physical phenomena as a single database.
Links to the ODM blank schema, tutorials on loading data into the ODM, and additional documentation can be found below in the Downloads and Additional Information section. In general, the creation of an ODM involves populating the already created schema with observations data. Because the ODM is a relational database, the relationships between each of the tables must be preserved as they are populated. Thus, the tables must be loaded in a specific order, with the most dependent tables being loaded last. This is discussed in more depth in the linked tutorials: Creating an Observations Data Model Using Microsoft Access and Merging Data from Two or More Observations Data Models.
Using an ODM in ArcGIS
Once an ODM has been populated with relevant observations data, it can be used in ArcGIS to investigate answers to hydrologic questions in a geospatial framework. The following examples will use a modified product of the two linked tutorials- a merged ODM database with water quality data from both an individual researcher and a state agency along the Texas coast. The data in this database has been limited to the year 2000 for simplicity sake. The modifications include the removal of sites that do not have values associated with them in this example.
Export the Sites table to a Feature Class
- In ArcCatalog browse to the location of the ODMinArcMap example database. This database is the modified product of the “Merging Data from Two or More Observations Data Models” tutorial. Note: this tutorial uses ArcGIS 9.1.
- Right-Click on the Sites table and select Create Feature Class/From XY Table.
- In the Create Feature Class From XY Table window, the X field and Y field should be automatically filled with Longitude and Latitude. Change the output file type to Shapefile, and change the name of the file to MergedODMSites.shp.
- Click OK.
Add ODM tables and shapefiles to ArcMap
- In ArcMap open a new map and Save As “ODMinArcMap.mxd”.
- Add Data
, and select the Sites,
Variables, Sources and Values2 tables. The “Values”
table from the ODM 3.0 schema has had to be renamed to “Values2” because
the term “Values” is reserved within ArcGIS. Additional tables could be
added as well. However, these are some of the most important ones, and
will suffice for this example.
- For a spatial reference, add the orthographic imagery from the Geography Network Explorer. In ArcMap go to File/Add Data From Internet/Geography Network. Search for “TNRIS” (Texas Natural Resources Information System) and under the link to “Simple DOQQ Mapservice for Texas, UTM Zone14” click “Add to ArcMap.” Note: this step is optional. It only provides additional geospatial reference.
The Table of Contents source view should now look something like the following:
Create the appropriate Relates between the tables and shape files
|
Source Table/Feature |
Source Field |
Related Table/Feature |
Related Field |
|
Values2 |
SiteID |
MergedODMSites |
SiteID |
|
Values2 |
VariableID |
Variables |
VariableID |
|
Values2 |
SourceID |
Sources |
SourceID |
|
SeriesCatalog |
SiteID |
MergedODMSites |
SiteID |
|
SeriesCatalog |
VariableID |
Variables |
VariableID |
For each of the above relates, complete the following procedure:
- Right-click on the Source Table/Feature. Select Joins and Relates/Relate.
- In the “Relate” window, select the appropriate tables and fields according to the table above. The following screen capture was used for the first relate between Values2 and MergedODMSites. Choose and appropriate name for each relate.
Once all the layers have been imported, and relates created, the user can query the data either by attribute or spatially. Data can be retrieved from the ODM using any type of SQL query in any one of a number of applications. However, the use of ArcGIS to view and query data from the ODM extends the spatial utility of such searches.
Determine variables measured at the mouth of the Nueces River
- Browse on the map to the mouth of the Nueces River. Most of the sites in this example are from the Nueces River or Canadian River. The Nueces points are those in the South-East portion of Texas. Select the point that appears to be at the mouth of the Nueces River. Alternatively, one could Select by Attributes using MergedODMSites as the selection layer and “"SiteID" = 12960” as the selection criteria.
- With point 12960 selected, Open Attribute Table and Show Selected.
- Go to Options/Related Tables/SeriesCatalog
- In the SeriesCatalog Attributes table, show the Selected records. Notice that there are 26 records selected. Each of these record is a unique combination of a site and variable. In this case, each of these 26 records is a variable measured at SiteID 12960. The “Variable” field describes the variable, and the ValueCount is the number of measurements at that specific site, of a specific variable. Note: the records used in this example include only those measured in the year 2000.
Find all Values for a particular site, and select a single Variable
- With the site with SiteID 12960 still selected, go to Options/Related Tables/Values2 in the Sites attributes table.
- The Values2 table will appear. Show only Selected. All the values measured at the mouth of the Nueces river will be shown in the table.
- Right-click on the heading of Variable field and select Sort Ascending. This will group all the values for a single variable together. Select only those records with a VariableID = 10 and OffsetType = 0.3. These four measurements are all water temperature, in degrees Celsius, measured a 0.3 meters below the water surface at the mouth of the Nueces River. These values can then be exported to another program for further data analysis, or graphed within ArcMap itself.
Conclusion
With the ODM tables and Sites shapefile added to ArcMap, the ability to query ODM data in a spatial context is greatly improved. It is possible to see how the various sites fit together geographically, and to select data based on geographic position. Because the ODM is a model that can be applied to many different types of observations data, additional sources of data can easily be added to what has been presented here. This has been only a brief example of some of the capabilities that exist with the combination of ArcMap and ODM 3.0. With future versions of the ODM and of ArcGIS, capabilities are sure to be increased.
References
Tarboton, D.G., Horsburgh, J.S., Maidment, D.R., and Jennings, B. “CUAHSI Community Observations Data Model Working Design Specifications Document- Version 3.” June 23, 2006.
Downloads and Additional Information
Observations Data Model Information
CUAHSI Community Observations Data Model Working Design Specifications Document- Version 3 (.pdf)
Tutorials
Supporting Files for Using an ODM in ArcGIS (.zip)
Creating An Observations Data Model Tutorial
Merging Data from Two or More Observations Data Models Tutorial