GEOG 6165 Web GIS

Create a web map to illustrate water use in Nevada

Introduction

Web maps are an excellent platform for sharing information, especially concerning issues that are interesting to the general public. They allow the audience to interact with, as well as visualize, data. For this project ESRI’s ArcGIS JavaScript API and public data on water consumption were utilized to create an engaging web map on water use in the state of Nevada.

  • The map should include several features:

    • A basemap for the region

    • A layer showing county boundaries

    • A layer list with various attributes

    • Pop up feature. The pop up should include information on water consumption per person, percent of total Nev water consumption, percent residential, agriculture, commercial

    • A search bar

    • A legend

  • Project data to an appropriate CRS for the study area

Data

Interpreting and Manipulating data

Data was provided related to water use in Nevada from 2010(Fig.1). The data was provided in tabular format and broken down by sector and county. The numbers in Figure 1 relate to the percent of total water consumption in each county per sector. The first five columns (STATE, STATEFIPS, COUNTY, COUNTYFIPS, FIPS) all refer in increasing fineness of scale to the location. FIPS is a numeric system for numbering states and counties to provide unique ID’s for each county. TP-TotPop is the total population, by thousand, per county. TO-WTotl refers to the total water consumption by county. Information is provided for four sectors of the population and their water consumption, see below:

  • Domestic - PSPtot

  • Agriculture - IRPtot

  • Golf Courses - IGtot

  • Mineral Industry - MIPtot

 
Fig. 1 Data provided related to Nevada water consumption. The first 6 columns are related to the county location. TP-TotPop refers to the number of people by thousands. TO-WTotl notes the number of millions of gallons each county uses. PerPWC is…

Fig. 1 Data provided related to Nevada water consumption. The first 6 columns are related to the county location. TP-TotPop refers to the number of people by thousands. TO-WTotl notes the number of millions of gallons each county uses. PerPWC is the number of gallons each person consumes per day. IRPtot, PSPtot, IGPtot and MIPtot all denote the number of millions a gallons used in agriculture, domestic use, golf irrigation and mining respectively per year.

 

These sectors do not account for the total water use in each region, so it was necessary to do some calculations to extrapolate the percent of the total each industry represented.

Methods

In order to create a useful web application showing water consumption rates in Nevada it was important to derive some additional figures from the data provided. The first was to establish what percentage of the total each of the four sectors, for which data was provided, represented of the whole water consumption for each county. Figure 2 represents the distribution of water consumption rates throughout Nevada.

  • (Total/Sector)*100= % per sector

It was also important to understand the water consumption per person in each county. Water consumption in each sector is represented by millions of gallons, the population figure is number of thousands of people per county. The below equation was used to normalize the figures and determine the consumption, in gallons, per person.

  •   Created a layer for consumption per person

    •      (Total*1000000)/(Pop*1000)= Use per person

Fig. 2 Map of Nevada water use by county and sector

Fig. 2 Map of Nevada water use by county and sector

Once the additional figures were generated, the tabular data was joined to a spatial file containing the county boundaries. The join was done using the unique ID for each county which was an attribute of the spatial data. This join created a layer that could then be published to ArcGIS Online as a MapServer for ingestion in ArcGIS API for JavaScript. The MapServer was read into the ArcGIS API for JavaScript as five different layers, each one symbolized on a blue graduated color scheme based on a different water consuming sector from the dataset.

Several other features were added to assist the user as they navigated the page. A search bar was included to allow site visitors to search for specific locations. Zoom widgets, a layer list and a legend were also added to the web page, see Figure 3. A pop-up feature was also coded into the web app to allow the user to select a county and receive a dialog window with details of the layer, such as county name and consumption amounts.

Results & Discussion

The aim of this project was to create a comprehensive web map that contains the following features (Figure 3) :

  • Five different layers showing the use by sector and a total use per person by county

  • Blue color scheme and natural breaks over 5 different groupings

  • Layers published as a MapServer

  • Used MapServer to create:

    • Layer list

    • Legend

    • Visual display

  • Created a search bar to query addresses 

  • Created a popup display to show water use data based on county

Fig. 3 Screen shot of final web map. The site is no longer active as the server hosting the script and data has been disabled. All symbolization pictured here is from the initial launch of the website.

Fig. 3 Screen shot of final web map. The site is no longer active as the server hosting the script and data has been disabled. All symbolization pictured here is from the initial launch of the website.

Publishing as a MapServer allowed for styling elements to be applied within ArcMap and then pushed to the web application. The layer list enables users to toggle between various data layers to visualize different sectors of Nevada’s economy as well as consumption per person. The pop-up encourages users to interact with the data and explore how water use changes from county to county.

As one of the driest states in the US, Nevada’s population is very concerned with water availability and consumption. The resulting web map performs the initial goal of this project, to convey information about water consumption rates in Nevada to a wider audience. As shown in Figure 2, rates of water use vary across the state. Clark county, which contains the most populous city, Las Vegas, has the greatest disparity between domestic consumption and other sectors. More rural counties in the northeast have higher percentages of water use in irrigation compared to other sectors. Interestingly, irrigation for golf courses does not form any significant portion of water use in any county.

Conclusions

Web maps are a great tool for sharing information and analysis to a wide audience. The ArcGIS API for JavaScript enabled publication of this information in a different format than a traditional map, such as Figure 2, with some effort taken to make the information more intuitive for viewers. Web apps have the potential to convey more information than static maps, as users are able to toggle between data layers and interact with information for each layer.

While there are many advantages to this format, there are several areas where this project would benefit from further development. Some styling elements from the ArcGIS environment, such as the eye symbol in the layer list and naming conventions, are not necessarily intuitive. Publishing as a MapServer brings over all the components of the map created in ArcMap, including field names designated from the data which could be confusing to the viewer. Effort must be taken to modify these components to something that is more informative to the end user. For this map, the styling was done to reflect the millions of gallons used per sector by county. It might also have been informative to create another visualization that reflects percentage of total use, rather than number of millions of gallons.

To view JavaScript code, click here.

MSGIS Program Skills

  • GIS Analysis

  • Spatial Data and Algorithms

  • GIS Workflow

  • Cartography and Graphic Design

  • Communication Skills

  • Basic Programming or Scripting (HTML, CSS, Javascript)