Introduction:It is very important to establish and understand the relationship between field work and ArcGIS. Properly utilized, ArcGIS can enhance the work being done in the field; failing to utilize ArcGIS properly can actually create more difficulty in the collection and transmission of data captured in the field.
The basis for a good relationship between ArcGIS and field work can be condensed down to pre-planning. Taking the time to develop the needs of your project and mold ArcGIS tools around those needs is essential to efficient and accurate data collection.
One of the keys to building this relationship is geodatabase construction. In preparation for the creation of a microclimate map of the UWEC campus, this exercise will focus in building a properly formatted geodatabase considering all the variables associated with the project. After providing some general information about a geodatabase, I will go over each of these two elements, pre-planning and geodatabase construction, in detail.
When importing spatial and attribute data into ArcMAP, it must be "contained" in something that the program can read and display.
Two different formats exist to do this: geodatabases and shapefiles.
Shapefiles (.shp) were originally created in the 1990's for use with the original ESRI program called ArcView. They store the primitive geometric data types of points, lines, and polygons. However this format lacks the capacity to store topological information. In other words, they do not possess the ability for the user to specify rules and conditions pertaining to the data. Pertaining to field work, this makes it much more time consuming for an operator to monitor the data collection process in order to avoid errors. As a general rule, shapefiles are larger, slower and less flexible than file geodatabases.
Geodatabases (.gdb), store the same type of information found in shapefiles as feature classes and can contain many such classes. In addition to being smaller, faster, and more flexible, geodatabases have one major advantage over shapefiles, the ability to utilize data management capabilities offered in ArcMAP. Topological information (rules) can be applied to the geodatabase, and each feature class within it, based on the range and type information they will contain.
This acts as a management tool for data being captured in the field. For instance, if the range of a particular type of data is well known, the range can be applied to a feature class essentially disallowing numbers outside of this range. This can help to avoid data entry mistakes while doing field work.
Five reasons to use geodatabases have been outlined by ESRI as listed below:
- A geodatabase is a uniform repository for geographic data, and it is scalable. This makes it easier to manage and access.
- Data entry and editing are more efficient. By storing GID data in a geodatabase, you are able to apply rules and constraints on the GIS data to reduce the chances of error being introduced into the datasets.
- The geodatabase can model advanced spatial relationships. The geodatabase not only defines how data is stored, accessed, and managed, but it can also implement and model spatial relationships of features in a feature class or between feature classes.
- The geodatabase has multiuser capabilities. You can have two or more users accessing the data at the same time, simultaneously making edits.
- The geodatabase enables your GIS data to be integrated with information technology systems.
Because of the advantages offered through the use of a geodatabase, they are an invaluable tool for fieldwork if properly employed. This is entirely contingent upon careful pre-planning by operators. Careful analysis should take place defining the scope of all data pertaining to the mission.
To guide thinking for the pre-planning process as it pertains to geodatabases, think in terms of domains, ranges, and measurement units.
These are the categories used in ArcMAP for geodatabase creation and will be discussed further in the next section, Geodatabase Construction. For now, just think of a domain as the general kind of data being collected (tree diameter, hill slope, wind direction, etc.), and ranges as the bounds that can be applied wherein all data collected will fall. Measurement units should be much simpler to understand, still it is important to specify how your data is being measured. Is distance being measured in meters or feet?
While this is not an exhaustive list of questions to be asked, the following can act as a guide for how to engage in pre-planning for the purpose of constructing an effective geodatabase.
What are the variables (domains) pertaining to your mission?
Can the data collection of these variables be bounded into a range of possible entries?
What are the measurement units for each variable?
If the variable records nominal data can it be grouped into categories?
Specifying the answers to these questions will provide you with the information you need to build an effective geodatabase.
Microclimate Pre-Planning Example
To provide an idea of how pre-planning for a geodatabase should be carried out. I will answer the questions I have listed and provide answers pertaining to the microclimate geodatabase I am preparing for use in a future exercise.
In the following weeks, I will be building a microclimate map of the UWEC campus. This will be done by measuring designated variables at various locations on campus and entering their records into a GPS device. In order to ensure accurate and efficient data collection, I will build a geodatabase with my specified domains and fields. This information will be imported to the GIS device. I will then be able to enter my data into pre-assigned fields based on my planning.
What are the variables (domains) pertaining to your mission?
Because my mission will be to create a microclimate map, I will be identifying weather-related variables to be entered as domains.
The variables I have identified are group name or number, temperature, time of day, wind direction, wind speed, relative humidity, dewpoint, and snow depth.
*It is also a good idea to include a general notes field for any information that does not fall into your variable categories.*
Can the data collection of these variables be bounded into a range of possible entries?/
What are the measurement units for each variable?/
If the variable records nominal data can it be grouped into categories?
Some data may not be numbers but nominal data. For instance, wind direction data will not be entered as a number but in words like northeast or southwest. Other information for other studies may be categorical in nature such as identifying how many of a certain kind of tree are in a certain area. Then, you would want to establish the potential range of categories. In Eau Claire, WI desert cacti can be ruled out as a potential category.
Once you have identified these elements pertaining to the data for your mission, you can proceed to building a geodatabase. I will explain this process in the next section.
Any time you are working with a new tool, becoming familiar with terminology, definitions, and locations can often be an arduous process. Building a geodatabase is a relatively simple process once you have become familiar with the basics. If it seems difficult at first, it is most likely just a matter of allowing yourself time to acclimate to what you are doing.
First, the program in which to set up a geodatabase is ArcCatalog. Open this program to begin.
Create a New File Geodatabase
Step 1: Within the catalog tree to the left of the screen, right click on the folder connection you would like to store the new geodatabase in. Select New and File Geodatabase (as seen in Figure 1).
Figure 1: This figure outlines the steps in ArcCatalog to take in order to create a new geodatabase.
Step 2: You will then have the opportunity to name your geodatabase (as seen in the highlighted area in figure 2). As a general rule avoid long names and spaces. In order to create space between two items, use underscore instead.
Figure 2: This figure shows the area where you can enter the name of your geodatabase (as seen in the highlighted area).
Step 3: Next, you want to enter the domains you defined in your pre-planning as well as specify ranges and units of measurement for each domain. To do this, first right click on your newly created geodatabase, and select properties.
Figure 3: This figure shows you how to select Properties in order to be able to enter your domains from pre-planning.
Step 4:The Database Properties screen will appear (as seen in Figure 4). Select the Domains tab at the top-left of this screen and you will be able to enter your domains.
Figure 4: This figure shows the layout of the Database Properties screen. This is where you will enter your domain information.
Step 5: To begin entering your domains start in the Domain Name field. Here you want to include a general title based on the variable. The Description area can include any information that helps you define the variable. Think of what you might want to remember when you are collecting data. For instance, I am not used to thinking in military time when recording the time. I will be setting the range up in way where military time is required. To ensure I remember that in the field, I have included that information in the description (as seen in Figure 5).
Figure 5: This figure shows the domain names and descriptions entered for the microclimate geodatabase. The domain name is the general description of the variable; the description can contain any information pertinent to you in the field.
Step 6: Next, move down the screen in the same database properties window to choose your Field Types. This exact term has not been previously mentioned but pertains to both the range and measurement unit specifications developed in pre-planning.
When you click on the default setting, text, to the right of Field Type, a drop-down menu will appear containing the following seven options: short integer, long integer, float, double, text, and date. Four of them relate to specific types of numerical data. Examples and applications pertaining to each data type are available from ESRI (as seen in Figure 6).
Figure 7: This table from ESRI outlines the range of usage for the four numeric data types.
Two data types are not included in this table because they are not for numerical data. I will explain their uses below.
Date: This data type is self-explanatory. However, it can include dates, times or dates AND times. The default setting for this data type consists of mm/dd/yy and hh:mm:ss fields for date and time, respectively.
Text: While this may also seem self-explanatory, the text field can include both letters AND numbers for use in recording street names, etc. It can be used for any variable not identified with numeric values.
Another option is to "code" textual information with numeric values to save storage space in the geodatabase. In order to take this step, pre-planning must include setting up an accurate coded system.
Step 7: If you have specified any ranges to bond your data by, you can do this by selecting the field to the right of Domain Type. A drop-down menu will allow you to select either coded values or range. Coded values is the default setting. By choosing range, a space for Minimum Value and Maximum Value becomes available (as seen in Figure 8).
Figure 8: This figure shows the minimum and maximum value field appearing below domain type when the domain type is switched to range.
Step 8: If you have chosen to included coded values for any of your domains you can enter them at the bottom of the database properties screen in the coded values table. Make sure the appropriate domain name is active when you do this or you could apply it to the wrong domain. In the Code field, specify the number attached to a certain value or category. Under the Description heading, specify the exact values attached to the code (as seen in Figure 9).
Figure 9: At the bottom of this figure entries for coded values can be seen including the code and description.
Step 9: You now have completed all the step necessary for the creation of your geodatabase. Simply select Apply at the bottom right of the Database Properties.
Create a Feature Class in ArcCatalog
Step 1: Right click on your new geodatabase; navigate to New, and Feature Class (as seen in Figure 10).
Figure 10: This figure outlines the process of creating a new feature class within your database in ArcCatalog.
Step 2: A window will appear allowing you to name your new feature class as well as set the Type of features you would like to be stored in the feature class in the drop down menu (as seen in Figure 11). The type of features you choose should be based on the way your data will be displayed on a map. If you will simply be storing point data, choose point features, if you are outlining building locations and basic area, choose polygon features, etc.
Figure 11: This figure shows the New Feature Class screen. Here you will enter the name of your feature class as well as set the feature type from the drop-down menu under Type.
Once this has been completed select Next at the bottom-right of the New Feature Class window.
Step 3: The next screen that will appear allows you to choose a coordinate system in which to display your data when you are ready to map (as seen in Figure 12). It is very important to choose a coordinate system that displays your particular area the best way possible. The UWEC campus is located in Eau Claire, WI will be best viewed in the NAD 1983 UTM Zone 15N and will be used to display my microclimate map.
Figure 12: this figure shows the screen where you will select the coordinate system to display your new feature class. More details about the coordinate system you select are listed under Current Coordinate System at the bottom of the screen.
Once you have selected your coordinate system, choose Next at the bottom-right of the Feature Class Properties window.
Step 4: The next screen will allow you to adjust the XY tolerance if you so desire. For this exercise, no changes were needed. To move from this step, select Next at the bottom-right of the Feature Class Properties window.
Step 5: The next screen will allow you to specify the database storage configuration. In most cases, you will choose the Default setting. To move from this step, select Next at the bottom-right of the Feature Class Properties window.
Step 6: The next screen to appear will have headings of Field Name and Data Type at the top (as seen in Figure 13). Underneath these headings you will place your Domain categories and their coinciding data types.
Figure 13: This figure shows the table where you will enter the domains and data types specified when you created your geodatabase based on your pre-planning.
When you have entered all of your domains and field types, click Finish at the bottom right of the New Feature Class Window. This new feature class will be used, through ArcPad, on the GPS unit to record data in the field. In my case, it will be used for the collection of data for a microclimate survey of the UWEC campus.
View Feature Class in ArcMAP
To give an idea of what information will look like once it has been collected, open ArcMAP.
Step 1: Open the Catalog in ArcMAP, and locate your newly created geodatabase and feature class (as seen in Figure 14).
Figure 14: This figure shows how to locate your new geodatabase and feature class (selected in blue to the far right of this screen). Simply drag it over to the table of contents to place the data on your map.)
Step 2: Drag your selected feature class to the Table of Contents on the left. From here you can look at the data tables you have created.
Step 3: Right click on your feature class in the Table of Contents to left of the screen and Select Open Attribute Table from the drop-down menu (as seen in Figure 15).
Figure 15: This figure shows how to access the attribute table for your new feature class.
Step 4: The attribute table that opens will contain all of the domains you created when building your geodatabase and feature class (as seen in Figure16). This is where all information will be displayed based on your collection through ArcPad on a GPS unit in the field.
Figure 16: This figure is the table displaying all of the domains you created in your geodatabase and feature class. All data collected in the field will be displayed here as it is collected in the field by inputting it into ArcPad on your GIS unit.
The geodatabase is an incredibly powerful tool for implementing pre-planning into actual field work. By carefully thinking out the needs of your project, you can build an intricate framework for the collection of data in your geodatabase.
Taking the time to familiarize yourself with building good database structure can be one of your greatest assets in the field. It will help keep you organized, increase efficiency, and improve accuracy of data collection. Without a carefully developed geodatabase, you will leave yourself prone to situations exactly opposite of the benefits it provides.