Querying Data And Understanding Spatial Relationships

 Querying Data And Understanding Spatial Relationships


This post is going to incorperate two online ESRI tutorials which helps understand querying data and working with spatial relationships. The two tutorials are called "Querying Data Using ArcGIS Pro" and "Understanding Spatial Relationships"

Querying Data Using ArcGIS Pro

Working with a large dataset can be overwhelming because the size of the data can slow your analysis. With ArcGIS, you can query a dataset to find the features that you need and even export these features to a smaller and more manageable dataset. Most GIS data includes features and an attribute table. The features correspond to locations of objects on a map. The attribute table provides descriptive details about the features. This information is referred to as the attributes of the feature. You can use these attributes to search and query your data. When you query features based on its attributes, it is referred to as an attribute query. Attribute queries have three basic components: an attribute field, an attribute value, and an operator.

Figure 76: Example of Attribute Table



Working With Data:

Download your data and open it in ArcGIS. The project includes a map that illustrates the location of health care facilities throughout Washington.

Figure 77: Health Care Facilities In Washington


Before you query the health care facilities data, you must identify the fields that you will use to build the query. In the Contents pane, right-click Health Care Facilities and choose Attribute Table. The columns in the attribute table represent the data's attribute fields. The rows in the attribute field represent individual features on the map. We will use two of these attribute fields to query the data.

Figure 78: Health Care Facilities Attribute Table


Now that we have identified the attribute fields we will build the attribute queries. The first query will select all health care facilities that are hospitals. We create attribute queries using the Select Layer By Attribute geoprocessing tool. This tool will create a selection of features based on the type of selection you choose and the query that you build.
  1. Click on the analysis tab
  2. In the geoprocessing pane, click tools
  3. Search for "Select Layer By Attribute" geoprocessing tool
  4. For Input Rows choose "Health Care Facilities"
  5. For Expression, click "New Expression"
  6. Complete the cause using the following parameters:
    1. Attribute Field: TYPE
    2. Operator: Is Equal To
    3. Attribute value: Hospitals
  7. Click Run

Now all the hospital features have been selected

Figure 79: All Hospitals Identified 


Next, we will identify which of these hospitals had the highest number of influenza cases. The next query will select all health care facilities with 200 or more cases of influenza in the past year. We will combine the first query with this query to select all hospitals with 200 or more cases of influenza.

  1. For input rows, make sure "Health Care Facilities" is selected
  2. For expression, click "Add Clause" 
  3. In the first drop down, confirm "And" is selected
  4. Complete the cause using the following parameters:
    1. Attribute Field: FLU CASES
    2. Operator: Is greater than or equal to 
    3. Value: 200
  5. Click Run

The features selected in the map are the hospitals that had 200 or more cases of influenza in the past year. In a real world application, these hospitals are the first health care facilities that you would visit to train about outbreak prevention.

Figure 80: Hospitals With 200 Or More Cases Of Influenza 



Understanding Spatial Relationships

You can solve real-world problems by understanding spatial relationships between different features. ArcGIS Pro has tools to help you determine the spatial relationships between features in your data. When visually analyzing a map, you will notice features and how they relate to each other. For example, which areas does a utility company gas line cross? Another example might be locating emergency facilities within a municipal boundary. The relationships between these features are known as spatial relationships, and they provide a visual perspective when solving spatial problems.

Working With Data:

Download the data and open it in ArcGIS. The project contains proposed wilderness areas in Utah. We will use these features to determine the acreage for the proposed areas. By looking at the map, you can determine that several proposed wilderness study areas are located in and around the San Rafael Swell. 

Figure 81: Proposed Wilderness Study Area


To better understand the amount of land being determined for wilderness suitability, you will first use the selection tools to select several wilderness study areas. 
  1. In the map tab, click "Select By Location" 
  2. In the dialog box, set the following parameters:
    1. Input features: Wilderness_BLMWSAs
    2. Selecting features: SanRafaelDesert
    3. Relationship: Within
  3. Click Ok
Figure 82: Selected Wilderness Areas


In the bottom right hand side, you can see that there are 38 wilderness areas selected. Using the selected features, we can use the statistics capabilities to get a sum of the total acreage.

  1. In the contents pane, right click Wilderness_BLMWSAs feature layer and choose Attribute Table, 
  2. scroll through the feature layer's available fields and values. 
  3. In the attribute table, right-click the WSA_ACRES field and choose Statistics. 
The Chart Properties pane opens, and a histogram displaying the distribution of WSA_ACRES is displayed below the map in the chart window. Chart properties used to define the chart's content are also displayed.

Figure 83: Field Acres Statistics 


You can see the total acreage sum for all wilderness areas in the state of Utah is 3,379,346 and the average sum for the selected area is 272,811 acres






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