*****  To join INSNA, visit  *****


I can only add: Listen to Tracy! She provides sound advice.

One major reason that I recommended starting with MapWindow GIS (free, 
open-source) is that it can serve as an excellent teaching tool for 
gaining experience with just the issues Tracy raises. In the 
"Documentation" link, you will find a link to a tutorial book, which you 
can download for a small price: "A Practical Look at MapWindown GIS", by 
Gary Watry and Daniel P. Ames. After Tracy's explanation, it will not 
surprise you to discover that after getting you started on a project, 
the next chapter deals with datum and projection. Think ahead to what 
you wish to measure in your resulting cartographic 

Best wishes,

Dr. J. B. "Jack" Owens, Ph.D.
Director, Geographically-Integrated History Laboratory
Research Professor of History, Idaho State University, USA
Lead PI, SOCNET Project, CDI, NSF (2009-2013)
Co-coordinator, DynCoopNet Project, TECT, ESF/NSF (2007-2010)
Guggenheim Fellow (2005-2006)
National Endowment for the Humanities Fellow (2004-2005)
E-mail: [log in to unmask]

On 3/8/2011 7:37 AM, Van Holt, Tracy wrote:
> *****  To join INSNA, visit  *****
> Don’t forget about the datums and projections!
> It is true that you can probably run some analyses without all of the projection/datum information and you may not need this information now or you may be working with clean data where everything happens to line up correctly.
> In the future though, you will likely want to run a more advanced analysis,  work with messy data, or want to collaborate with someone who can run more advanced analyses and this will require datums/projections. You will need datums/projections to add another layer on top of your map, extract information from other maps, or conduct advanced geospatial analyses. Many advanced geospatial analysis programs only take data that are in meters. To get your data in meters, you will need to re-project the lat/long data into a projection system and for that you will need the datum.  Depending on the type of analysis, you would change your projection.  Projections are specific for the type of analysis that you will run and they can preserve either distance, or shape, or area, or a little bit of each of those items.
> My long posts on this topic will point you to the basic information that you need to know at some point down the road.  When someone says to me that something doesn’t match up, where did my points go, or how come I can’t project, I immediately think that there is a datum/projection problem. It could be an issue with the network analysis software, but there are multiple factors going on.
> Tracy Van Holt
> East Carolina University
> [log in to unmask]
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Monday, March 07, 2011 4:52 PM
> To: Van Holt, Tracy
> Cc: [log in to unmask]
> Subject: Re: [SOCNET] Geospatial Tutorial Datums and Projections RE: [SOCNET] Geograpical Coordinates in NetDraw - please help!
> One note about Sonoma: it uses the GMT package for rendering maps and
> ties. This means that you can render your graphs without worrying about
> translating spherical coordinates to x,y coordinates. You can submit the
> coordinates of your actors via any number of latitude and longitude
> formats (decimal or degree:minute:seconds, postiive/engative values, or
> East/West coords).
> -Manish
>> There could also be a projection/datum issue or negative coordinates,
>> which become important as you try to overlay different datasets.  This is
>> the main reason why novice GIS users can’t get maps/coordinates to line
>> up.  Even if this isn’t the current problem you have, if you ever want
>> to match up your geospatial data with other maps, you’ll need to know
>> the basics. Here is some info I pulled from the ESRI (ArcGIS) site. They
>> have excellent help files that explain these concepts--it’s all about
>> datums, geographic systems, projected coordinates, and negative lat
>> /longs! You need to know the datum of your coordinates and of any system
>> that you want to project your coordinates into otherwise your points may
>> not project.
>> A datum defines the position of the spheroid (approximation of the earth)
>> relative to the center of the earth.  A datum provides a frame of
>> reference for measuring locations on the surface of the earth. It defines
>> the origin and orientation of the latitude and longitude lines. So  datum
>> tells you where the x,y of your lat/longs begin.
>> Today we are moving towards a universal datum WGS 1984, but there are
>> numerous datums out there.  In the link above you can see what happens if
>> you try to overlay points in different datums (sometimes the error is OK
>> and sometimes the error is not OK). People know enough to collect lat/long
>> points nowadays but they don’t understand that you need the datum as
>> well. I mapped out the official fisheries management areas in Chile to
>> find out that half of the management area located on the land if you used
>> the official coordinates! To get an idea of how many datums and geographic
>> coordinate systems are out there, you can see the attached file
>>   What do you do if you have lat longs and no idea what the coordinate
>> system is? First try WGS 84. If that doesn’t work, then you could guess
>> based on what people tend to use locally. In Brazil people use PSAD 1956.
>> In Chile, people use SAD 1969. In North America people use NAD 1927. Maps
>> should also have the datum and projection written on them, though most
>> don’t. Many cases there is metadata that has the datum/projection info.
>> This is true of satellite images that you may download or other
>> geospatially explicit datasets.
>> A geographic coordinate system is a three-dimensional spherical surface to
>> define locations of the earth (which is often confused with a datum). A
>> GCS contains the angular unit of measure, a prime meridian, and a datum
>> (based on a spheroid)
>> Finally you have projected coordinate system, which is a flat 2-D surface.
>>   Unlike a geographic coordinate system, a projected coordinate system has
>> constant lengths, angles, and areas across the two dimensions. A projected
>> coordinate system is always based on a geographic coordinate system that
>> is based on a sphere or spheroid.
>> Certain projection systems have particular datums associated with them. So
>> if you try to put lat long into a projected coordinate system, you need to
>> know the datums of both and transform the data so they are in equal
>> systems.  There are many projected coordinate systems out there. To get an
>> idea of how many see here.
>> Finally, if you are working in a place where you have a negative latitude
>> or longitude, you may have positive numbers written down instead of
>> negative numbers. Locally people say or even write down  the positive
>> number, even though the number is really negative. So you need to check if
>> you are working in a negative zone because this could also be a source of
>> error.
>> I hope this basic geospatial tutorial helps!
>> Tracy Van Holt
>> Assistant Professor
>> East Carolina University
>> [log in to unmask]<mailto:[log in to unmask]>
>> From: Social Networks Discussion Forum [mailto:[log in to unmask]] On
>> Behalf Of [log in to unmask]
>> Sent: Monday, March 07, 2011 1:18 PM
>> To: [log in to unmask]
>> Subject: Re: [SOCNET] Geograpical Coordinates in NetDraw - please help!
>> I can also recommend the Sonoma package that I presented at Sunbelt this
>> year. The package allows for geographic visualization of network data,
>> with fine tuned control of tie width and tie coloring, in addition to
>> integration with GIS packages like ArcGIS.
>> Best,
>> Manish Nag
>> Doctoral Candidate, Sociology
>> Princeton University
>> ----- Reply message -----
>> From: "Jamie Olson"<[log in to unmask]>
>> Date: Thu, Mar 3, 2011 10:33 am
>> Subject: [SOCNET] Geograpical Coordinates in NetDraw - please help!
>> To:<[log in to unmask]>
>> ***** To join INSNA, visit *****
>> Hi Stephanie,
>> I just want to add that ORA provides a bit more than just layout with
>> lat/lon.  There are also a variety of exploratory analysis features,
>> including spatial clustering w/feedback and sizing/coloring by network
>> structure statistics.  ORA also contains extensions of several standard
>> network centrality measures that take into account the spatial
>> information.
>> I think it's great that people have brought up visualization in Google
>> Earth.  ORA also allows export to KML, but I thought I'd mention a problem
>> I've come across.  Google Earth may not provide a truthful rendering of
>> lines at various levels of resolution.  They have a complicated caching
>> process that often results in a sort of flickering as you zoom in and out,
>> which I've found distracting.
>> I saw that Dr. Owens recommended MapWindow.  I don't have much experience
>> with MapWindow, which seems to be a fine product, but I noticed that it is
>> not a cross-platform tool.  If you need to or would like to work on
>> non-windows systems, there are a number of other open source GIS tools.
>> I've had about the most success with OpenJUMP<>,
>> but qgis<>  is also easy to use.
>> Good luck,
>> --Jamie
>> Jamie Olson
>> School of Computer Science
>> Carnegie Mellon University
>> 5000 Forbes Ave.
>> Pittsburgh, PA 15213
>> [log in to unmask]<mailto:[log in to unmask]>
>> On Thu, Mar 3, 2011 at 4:13 AM, Clement Levallois
>> <[log in to unmask]<mailto:[log in to unmask]>>  wrote:
>> ***** To join INSNA, visit *****
>> Hi Stephanie,
>> If you are still stuck with your geo layout, you can try:
>> - Gephi, which has a layout plugin for this purpose:
>> - ORA also provides a layout of long / lat coordinates I believe
>> Good luck!
>> Clement
>> ___________________
>> Clement Levallois, PhD
>> Erasmus University
>> The Netherlands
>> [log in to unmask]<mailto:[log in to unmask]>  |
>><>  | Twitter:
>> @seinecle
>> -----Original Message-----
>> From: Social Networks Discussion Forum on behalf of Eric DesMarais
>> Sent: Wed 02/03/2011 22:37
>> To: [log in to unmask]<mailto:[log in to unmask]>
>> Subject: Re: [SOCNET] Geograpical Coordinates in NetDraw - please help!
>> *****  To join INSNA, visit  *****
>> Since you have coordinate data, it sounds like the easiest thing to do
>> would
>> be to use GIS software such as ArcGIS, use your network visual as an
>> overlay, and stretch it to fit over the map, matching the coordinate data
>> of
>> your nodes to the coordinate data of the map.
>> It is exciting to see another doctoral student in social work using maps
>> and
>> networks.  Hope your project goes well.
>> --
>> Eric DesMarais, MSW, LCSW
>> Doctoral Student
>> Graduate School of Social Work
>> University of Denver
>> 2148 South High Street
>> Denver, CO 80208
>> 720-413-5809
>> On Wed, Mar 2, 2011 at 8:29 AM, Stephanie Smith<
>> [log in to unmask]<mailto:[log in to unmask]>>  wrote:
>>> ***** To join INSNA, visit *****
>>> I have been trying to figure out how to project the image of my network
>>> on
>>> to a map and have not been successful. I have the latitude and longitude
>>> of
>>> each node and have made them into attribute files so to place the nodes
>>> with
>>> their location on the map. However, once I'm in NetDraw and click on
>>> Layout/Coordinates as Attrbutes and try to complete the steps, my
>>> network
>>> vanishes! **Poof**
>>> Has this ever happened to anyone else? If so, do you know what I am
>>> doing
>>> wrong?
>>> Any help you could lend would be greatly appreciated.
>>> Thank you!
>>> Stephanie Smith
>>> PhD Student
>>> School of Sociology, Social Policy&  Social Work
>>> Queen's University Belfast
>>>   6 College Park
>>> Belfast BT7 1LP
>>> Northern Ireland

SOCNET is a service of INSNA, the professional association for social
network researchers ( To unsubscribe, send
an email message to [log in to unmask] containing the line
UNSUBSCRIBE SOCNET in the body of the message.