Posts tagged GIS

The figure above is a [very] simple model displaying isostatic rebound of Greenland if its ice sheet were not present. The Greenland ice sheet (GISh) is 2,500 km north-south, 1,000 km east-west, 3 km thick, and covers almost 2 million square kilometers (or 80% of the island). Because of the weight of GISh, the continental lithosphere is depressed in an elastic motion. If the GISh were to be removed, the lithosphere would rise in reaction. This rebounding process is known as isostasy and in case of ice sheets, glacial rebound. Underneath any vast ice sheet is a land surface not unlike any other ice-free surface on earth. It has valleys, hills, plains, etc. Therefore, we see that in Greenland the underlying topography, the Bedrock (or simply the Bed), is shaped as a concave, and with the removal of the ice sheet it rises and assumes a less curved form. PS: Please note that this is purely for visualization purposes and not to be used in scientific analysis.

The figure above is a [very] simple model displaying isostatic rebound of Greenland if its ice sheet were not present. The Greenland ice sheet (GISh) is 2,500 km north-south, 1,000 km east-west, 3 km thick, and covers almost 2 million square kilometers (or 80% of the island). Because of the weight of GISh, the continental lithosphere is depressed in an elastic motion. If the GISh were to be removed, the lithosphere would rise in reaction. This rebounding process is known as isostasy and in case of ice sheets, glacial rebound.

Underneath any vast ice sheet is a land surface not unlike any other ice-free surface on earth. It has valleys, hills, plains, etc. Therefore, we see that in Greenland the underlying topography, the Bedrock (or simply the Bed), is shaped as a concave, and with the removal of the ice sheet it rises and assumes a less curved form.

PS: Please note that this is purely for visualization purposes and not to be used in scientific analysis.

Day in the life of a GIS Analyst

 

An abbreviated version of a typical day involving the duties of a GIS Analyst and Developer. Or maybe it’s just me.

Hour 1

Arrive to work before the sun does. Grab some coffee, catch up on email. Peruse the latest ArcUser and ArcNews and look at how easy it all should be.

Hour 2

Crap, all the Arc licenses are in use. Send out mass email to all users asking if someone can free one up. Ok, you have a license. One of your SDE databases is down, a ticket to ESRI has been sent. Use an old slower SDE. Begin running a geoprocessing task on a couple million polygons.

Hour 3

More coffee. Discover some internal web applications are not working because that single SDE is down. Send out email to users notifying of situation. Development IDE of choice crashes or freezes a few times to remind you that you are a bad person.

Hour 4

ArcMap crashes in the middle of editing. Try again, crap, cashed again. Try this one more… forget it, no more editing, just use draw tools to make quick exhibits.

Hour 5

More coffee. Given a PDF map that came from a consultant and asked make changes. That’s it, just a PDF. You do things to make this happen that make you feel dirty.

Hour 6

Lunch time. Ninety-percent of solutions to GIS questions or development issues are found on web sites that are blocked as Social Media or Blogs. Twitter rant (vis smartphone). Check that geoprocessing task is still running.

Hour 7

Rush request for exhibit that needs data on the SDE that is down. That particular dataset can also be found on an external hard drive. The enclosure died last month. Pry open enclosure, rip out hard drive, pop open work pc and manually plug it in to extract the data. Cross your fingers that no one from IT department walks in as the internals of your gutted work machine are exposed.

Hour 8

Seriously reconsidering your life decisions.

Hour 9

Geoprocessing task failed around the 8-hour 5-minute mark with geometry errors. After 40 minutes is still cancelling itself. Go home and drink to forget.

Note: No actual analysis got done, as the failed geoprocessing task squashed that goal.

Source: Rene R.

odoe.net

The GeoNames Geographical Database

The GeoNames geographical database is available for download free of charge under a creative commons attribution license. It contains over 10 million geographical names and consists of 7.5 million unique features whereof 2.8 million populated places and 5.5 million alternate names. All features are categorized into one out of nine feature classes and further subcategorized into one out of 645 feature codes. (more statistics …). 
The data is accessible free of charge through a number of webservices and a daily database export. GeoNames is already serving up to over 20 million web service requests per day.

GeoNames is integrating geographical data such as names of places in various languages, elevation, population and others from various sources. All lat/long coordinates are in WGS84 (World Geodetic System 1984). Users may manually edit, correct and add new names using a user friendly wiki interface.

geonames.org

MIT Releases Free GIS Toolbox


The City Form Research Group is releasing a state-of-the-art toolbox for urban network analysis. As the first of its kind, this ArcGIS toolbox can be used to compute five types of graph analysis measures on spatial networks: Reach; Gravity; Betweenness; Closeness; and Straightness. 

The tools incorporate three important features that make them particularly suited for spatial analysis on urban street networks. First, they account for geometry and distances in the input networks, distinguishing shorter links from longer links as part of the analysis computations. Second, unlike previous software tools that operate with two network elements (nodes and edges), the UNA tools include a third network element - buildings - which are used as the spatial units of analysis for all measures. Two neighboring buildings on the same street segments can therefore obtain different accessibility results. And third, the UNA tools optionally allow buildings to be weighted according to their particular characteristics - more voluminous, more populated, or otherwise more important buildings can be specified to have a proportionately stronger effect on the analysis outcomes, yielding more accurate and reliable results to any of the specified measures.

The tools are aimed at urban designers, architects, planners, geographers, and spatial analysts who are interested in studying the spatial configurations of cities, and their related social, economic, and environmental processes. The toolbox is built for easy scaling - it is equally suited for small-scale, detailed network analysis of dense urban areas as it is for sparser large-scale regional networks.  The toolbox requires ArcGIS 10 software with an ArcGIS Network Analyst Extension. (via SpatialBroadcast)

study-the-city

The organized chaos of my desk at work.

The organized chaos of my desk at work.

This month marks my one year anniversary working at the Lamont-Doherty Earth Observatory of Columbia University. One of the earliest projects I’ve been working on was the Antarctica’s Gamburtsev Province (AGAP). The figures above display the bedrock topography of central Antarctica under the East Antarctic Ice Sheet. The “Before” figure is a subset of the digital elevation model of Antarctic bedrock created by the British Antarctic Survey (BAS) using data from surveys from the past 50 years. BAS is currently working on a second version of BEDMAP. The “After” figure displays a grid of study area using data collected during AGAP. As you can see, AGAP provided the scientific community with previously unknown topographic detail of the Antarctic bedrock. Both “Before” and “After” figures have outline vectors of the AGAP survey flights overlain. Here is a quick primer on the AGAP project: During the International Polar Year 2007 – 2009, scientists from six nations collaborated on a multi-disciplinary investigation of the Gamburtsevs, the least explored mountain range on Earth buried beneath the East Antarctic Ice Sheet, as part of the Antarctic Gamburtsev Province (AGAP) project. The AGAP project collected more than 120,000 line km of new aerogeophysical data using two Twin Otter aircraft.  Data included ice penetrating radar, magnetometer, gravimeter and laser altimeter measurements. The main AGAP survey grid included north-south lines spaced 5 km apart, with crossing lines every 33 km and transects over the Vostok Subglacial Highlands, South Pole and southern Recovery lakes region. 150-MHz ice penetrating radars with bandwidths of 15 to 20 MHz measured ice thickness, bedrock topography, sub-ice hydrology, and produced high-resolution images of the internal structure of the East Antarctic Ice Sheet. Magnetic data map geologic structures across the mountain range, while gravity data provide new insights into the tectonic evolution and crustal thickness of the region. A swath-scanning laser altimeter with a spatial resolution of 2 meters measured elevation and details of the ice surface.

This month marks my one year anniversary working at the Lamont-Doherty Earth Observatory of Columbia University. One of the earliest projects I’ve been working on was the Antarctica’s Gamburtsev Province (AGAP).

The figures above display the bedrock topography of central Antarctica under the East Antarctic Ice Sheet. The “Before” figure is a subset of the digital elevation model of Antarctic bedrock created by the British Antarctic Survey (BAS) using data from surveys from the past 50 years. BAS is currently working on a second version of BEDMAP. The “After” figure displays a grid of study area using data collected during AGAP. As you can see, AGAP provided the scientific community with previously unknown topographic detail of the Antarctic bedrock. Both “Before” and “After” figures have outline vectors of the AGAP survey flights overlain.

Here is a quick primer on the AGAP project:

During the International Polar Year 2007 – 2009, scientists from six nations collaborated on a multi-disciplinary investigation of the Gamburtsevs, the least explored mountain range on Earth buried beneath the East Antarctic Ice Sheet, as part of the Antarctic Gamburtsev Province (AGAP) project.

The AGAP project collected more than 120,000 line km of new aerogeophysical data using two Twin Otter aircraft.  Data included ice penetrating radar, magnetometer, gravimeter and laser altimeter measurements. The main AGAP survey grid included north-south lines spaced 5 km apart, with crossing lines every 33 km and transects over the Vostok Subglacial Highlands, South Pole and southern Recovery lakes region. 150-MHz ice penetrating radars with bandwidths of 15 to 20 MHz measured ice thickness, bedrock topography, sub-ice hydrology, and produced high-resolution images of the internal structure of the East Antarctic Ice Sheet. Magnetic data map geologic structures across the mountain range, while gravity data provide new insights into the tectonic evolution and crustal thickness of the region. A swath-scanning laser altimeter with a spatial resolution of 2 meters measured elevation and details of the ice surface.

A First Visit to North Greenland - Part II (Science Mission Over Greenland’s North Glaciers)

Part I

Our science mission on Monday, May 9th involved flights over the north and northwest of Greenland, specifically the Steensby, Ryder and Hagen glaciers as well as the Fald Ice Cap in Kronprins Christian Land. The Steensby Glacier passes through the Sherard Osbron Fjord, while the Ryder Glacier is constrained by the Victoria Fjord. This was my first flight on the P3 and the scenery was nothing short of breathtaking. I found the sheer dimensions of the fjord cliffs particularly interesting. Fjords are visual testaments to the dynamicity of our planet. The fjords in north Greenland were quite steep, at almost 90o, and appeared to be carved with surgical precision. These were formed in the last glacial period as Greenland was covered with ice and snow, the weight of which depressed the crust and glaciers cut through surrounding rock. Since the end of the last ice age, a phenomenon called ‘crustal rebound’ took place, in which the formerly depressed land masses slowly rose. This process is called isostasy, and it has resulted in those awe-inspiring cliffs.

Middle Ordovician – Lower Silurian cliffs surround the Sherard Osborn Fjord and the Victoria Fjord.

 Outside the scientific community, glaciers are sometimes thought of as ‘just a block of ice’, but quite frankly they are sort of landmasses in their own right and close to inland islands. They are solid, they are dynamic, and they have layers which attest to their existence. They have several surficial features, like crevasses, shown below. These are the equivalent to fractures in rock and are formed due to a combination of factors such as the disparity in the glacier’s speed and the stress generated by flow over an uneven terrain. Furthermore, the glacier’s lower layers are more malleable than its upper layers hence resulting crevasses.

Crevasses forming on the Ryder Glacier. The photo does not give justice to scale. These features are easily 100m wide.

- Part I