GIS, Imagery, Mapping

What is GIS?

Learning to read, my youngest daughter looked at her dad proudly as she shouted out the letters on his T-Shirt…“G I S!”. Then she looked at me inquisitively and said “Mommy, G I S?” I responded in the affirmative, “Yes sweetie, G I S!”

So, what is GIS?

This picture which I captured on my return flight to Montserrat, overlooking Davy Hill and Little Bay will help me to explain.

View overlooking Davy Hill and Little Bay, Montserrat

At first glance, buildings, roads, vegetation, hills and the ocean can be seen in my picture. GIS, which stands for Geographic Information System allows you to capture, store, manipulate, analyse, manage and present, this type of geographic data.

The unique aspect about GIS is that it allows you to store additional information, called “attributes”, about each feature. For example, attributes of a road may include its name, type, whether primary or secondary and its length. Similarly, attributes of a building, may include the owner’s name, a category of use, whether it is residential or commercial, the material that the building is made from, for example, wood or concrete, the roof type and also the number of floors.

Attribute data can be obtained from a number of sources or data can be captured specifically for your application. Spatial data can be obtained from satellite images, aerial photographs, scanned maps and similar resources. Essentially, any format of a geographical image with location or co-ordinate points can be used as spatial data.

The combination of spatial and attribute data gives GIS the capability of providing answers to complex questions. It is undeniably, the partnership of these two data types that enables GIS to be such an effective problem solving tool through spatial analysis.

To visualize large amounts of information interactively is one of the most attractive and useful capabilities of GIS. To do this, data is extracted and stored in the form of “layers”.  The image below captures graphically how these layers relate to the real world.

                           Representation of layers in GIS

GIS utilizes two primary data types: vector and raster. Vector data is represented as either points, lines, or polygons. So let’s go back to my picture of Montserrat. In that picture, the location of a particular facility, such as the new location of ZJB Radio in Davy Hill can be captured as a point, other buildings can be represented as polygons, along with the entire settlement area of Davy Hill and the roads can be captured as lines.

Contrastingly, raster data is best suited for information that does not have hard boundaries or locations. So again, let’s revert to the picture which I took. The hills and valleys which you can see are best represented as elevation or terrain modelling surfaces. Raster data is usually used to represent this type of data in a GIS. Data in rasters are viewed as a series of grid cells where each cell has a value representing the feature being observed. 

Unlike, traditional paper maps, GIS is fully interactive. It allows you to add new fields of data,  change the color scheme or form of the map, add text and move symbols around. GIS displays allows you to zoom and pan which offers new perspectives and new insights. These and a host of other capabilities give a user tremendous flexibility and power.

GIS is more than just software. It is a system where trained people and methods are combined with geospatial tools, to enable spatial analysis, manage large datasets, and display information in a graphical form.

GIS Day is celebrated annually, read more in my previous blog: https://lavernrogersryan.com/celebrate-gis-day-annually-and-dont-forget-the-cake/.

Lavern Rogers-Ryan is a geospatial consultant specializing in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.

Disaster Risk Reduction, Imagery, Mapping

Satellite Imagery is A Powerful Visual Aid in GIS and Disaster Response

The earthquake events of August 21, 2018 which shook Venezuela, Trinidad and other neighbouring countries (https://www.usgs.gov/news/magnitude-73-earthquake-venezuela) reminded me that not all disasters can be predicted or come with a warning. Videos which showed the impact of the earthquake quickly filled my social media timeline, causing me to reflect on the training I had undergone as project manager for the International Charter Space and Natural Disasters (https://disasterscharter.org). This organization, once registered with, provides a series of support through the use of satellite imagery to assist in the aftermath of a disaster.

Satellite imagery is a form of remotely sensed data with proves useful in the occurrence of an unforeseen event and provides a powerful visual aid when utilized with a geographic information system (GIS). Disaster risk managers are better able to assess their region’s risk when they are able to compare pre and post disaster images.  This type of analysis enables relief workers to identify changes in the landscape, such as buildings which are no longer standing and roads which are obstructed. It is an efficient way to identify damage and conduct rapid impact and needs assesments. GIS supports the use of satellite imagery to locate damaged facilities, identify the type and amount of damage and begin to establish priorities for action.

As satellite sensors improve, satellite imagery is becoming more useful. One of my favourite places to explore satellite data is the USGS Earth Explorer Portal (https://earthexplorer.usgs.gov/). It provides an interface where one can search the available sensors to see the data that is available for a particular area of interest. The advantage of the USGS Earth Explorer is that it houses data from the Landsat Programme which has a 40+ year track record of image acquisition. It allows for free downloading of data over chronological timelines while providing a long list of satellites to choose from.

Additionally, capturing my interest for hours on end is the USGS Earth Now Viewer (https://earthnow.usgs.gov/observer). This viewer is truly remarkable as it shows the position of the Landsat sensor in real-time. It also gives a visual of the satellite images being collected when the sensor scans the earth.

The Landsat Program began with Landsat-1 in 1972 and Landsat- 9 is planned for 2023. Over the years, Landsat has enhanced the number of spectral bands, spatial resolution and spectral resolution. Landsat 1-3 sensors collected data in only 4 bands and at 60 meter resolution. Over time, this has improved, as Landsat 8 now collects in 11 spectral bands varying from 15 meter to 100 meter.

The Sentinel Satellites of the Copernicus Programme also provide free satellite imagery which can be downloaded at the Copernicus Open Access Hub (https://scihub.copernicus.eu/dhus/#/home). The Sentinel-2 provides some improvement to the Landsat data with sharper imagery of up to 10 meters. Sentinel-2 monitors more frequently with a revisit time of 5 days and captures land changes in 12 spectral bands, each ranging from 10 – 60 meters pixel size. The USGS Sentinel2Look Viewer (https://landsatlook.usgs.gov/sentinel2/viewer.html) allowed me to browse through some sentinel-2 imagery. I found relatively cloud free imagery of Montserrat (shown below) which was acquired on 12th April 2018. This is a plus as cloud-free imagery is not always available due to our location and climate.

With the assistance of a skilled technician, satellite imagery can be utilized effectively in disaster management especially during the response stages. By combining spectral bands and performing image classification techniques the capabilities of remotely sensed data can be fully utilized in disaster management.

 

Lavern Rogers-Ryan is a geospatial consultant specialising in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.

Disaster Risk Reduction, GIS, Imagery, Mapping

Five (5) things GIS has taught me about Disaster Management

I am no stranger to the impact of disasters having survived Hurricane Hugo in 1989, and witnessed the Soufriere Hills Volcano disrupt everything I knew about life in Montserrat since 1995.

As I listened to the reports on the experience of our neighbouring islanders who were affected by the super hurricanes of 2017, Irma and Maria (which I now simply refer to as IRMARIA), I empathized.  Now as I watch reports of the experience of the residents of El Rodeo, Guatemala in dealing with the eruption of Volcan de Fuego which erupted on June 6, 2018, I am driven to share a bit of how my work can help countries manage disasters better.

Geospatial technologies have improved in recent years and are more efficient and reliable to enhance our planning, mitigation, preparedness, response and recovery from disasters.  The majority of data needed for these phases of emergency management is spatial, and once it is spatial it can be mapped and utilized effectively.

Over the years, Geographic Information Systems (GIS) has taught me a few things in relation to disaster management. Here are five (5) of them:

1.       Most emergencies don’t allow time to gather information.

2.       During an actual emergency there is no time for guessing or estimating, it is critical to have the right data, at the right time.

3.       Lack of appropriate information leads to poor planning and poor decision making.

4.       GIS provides a mechanism to centralize and visually display critical information during an emergency.

5.       GIS saves time, money and lives!

The road to recovery is often very difficult for anyone faced with loss after the impact of a disaster. Many of us on Montserrat however, built up our resilience as we reflect on the loss of homes – not just houses. We have embraced the challenge of recreating the places we lost. Unbelievably,  the Government Headquarters building in Plymouth was newly constructed and the Glendon Hospital was newly refurbished at the time of the eruption. Personally, I often reflect on the town centre which was thriving and bustling as it created jobs, enhanced livelihoods and held memorable spaces, such as “Evergreen Tree” and the “market” for social interaction.

A specialism in GIS allowed me the opportunity to support recovery efforts by utilizing data and producing maps that helped to manage evacuation paths, relocate families safely to shelters, assist in ash clean-up efforts by tracking progress and by utilizing the output of modelling scenarios to identify future impact areas.  GIS provides a mechanism to forge ahead and recover despite the impact of a disaster. Montserrat is now in a phase of re-development and GIS has contributed significantly to this. I do look forward to telling you more about how GIS can be used in disaster management.

 

Lavern Rogers-Ryan is a geospatial consultant specialising in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.