why people tends to use vario instead covariogram?

Well, based on my disucussion with prof Bogaert, there are several reasons why people tends to use variogram instead of covariogram. But before we discuss it, let us recall that variance (h) is equal to covar (0) – covar (h). So basically, the variogram is just the horizontal-twisted shape  of covariogram. This equation is true ONLY in the case od second order stationary.  While in non linear case this equation is not necessarily true. In spatial analysis though, the second order stationary is a priori assumed.

Using variogram instead of covario can be regarded as a matter of  “taste”. In time series case, people tends to use covariogram and may not even familiar with variogram, WHILE in spatial case, people tends to use the variogram. The second order stationary in spatial analysis makes the variogram easy to use, derive calculation, and intituively easy to understand.

Well if that so, why we still need covariogram? we still need covariogram to check the consistency of our dataset. As shown from the equation, if we have stable , consistence dataset ( at least until second order moment), the covariogram and variogram will be horizontaly-opposed one to each other.

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model builder

I did not realize how easy to use ArcGIS and IDRISI before i found modelBuilder. The simple way to explain ModelBuilder is it works as the way your brain works. It put everything in graphical model, and by simply click “run” button, you will see that this is not just an ordinary box as in visio or in chart in your M.Word. It really runs !! it runs the process using the input, and producing the output which again is used by other process, and so on so forth untill the end result coming. Amazing.

I would say model builder from IDRISI, ArcGIS, and ArcView principly the are just the same. the different is only on how we use it. In this post, i will focusing my discussion on using modelBuilder in ArcGIS.

in ArcGIS, you have installed modelBuilder, unlike in ArcView where you have to install spatial analyst, the only thing you should do is just make sure that your spatial analyst extention is checked. Then you ready to go.

modelbuilder

first, open your ArcToolbox. there you will find a whole bunch of tools use in ArcGIS inclusing famous RUSLE model to explore the soil erosion untill KRIGING methods for geostatistic. Everything is there!.

Btw, i forgot to tell you, why we should use model builder? why not we just use ordinary functions? The answer is modelBuilder offers a lot more easier process and each time you want to change something/parameters in one or all your process, you can easily done it simply by correcting it in one of your box. The modelBuilder is like the living flow chart!!.

ok, now after you open your ArcToolbox, right click and choose new toolbox. Then they will ask you to set parameters. Ignore this for a while, let us take the given value and continue to the main board of model builder.

Built-Up Density

Built-up density is important for planners like us. I remember when I made my final project titled Urban Fire Risk in Bandung. In my final project, one of the criteria to derive the risk index was by employing “population density”. The main problem is that this data were come in regional based, which mean it does not contigious and not so reliable. Population density every where in Indonesia is based on Kelurahan (village administrative unit). Density is caunted firstly by summing the population per village and divided with the total area of the the correspond village.

I read many article try to solve this problem by applying other demography instrument, one of it is by using built-up density. Built-up density is based on a though that population living in area must have a linier correlation with the place where he/she lives. In other words, buil-up density must have reflects the population density. The higher the population density, the more higher built-up density, or vice versa.

then, our question is, how to make the built-up density? simple. First think that you should have are;

1. installed ArcView and ArcGIS 8/9 with Spatial Analyst extention checked in your computer
2. Land use data in vector based
3. I use Xtools, additional tools for ArcView 3.3

How to make it? I will explain you the logic thinking behind all these functions before we go step-by-step through the functions. OK, the key is we will make the built-up density by using “density” function from spatial analyst ArcGIS. this function requires you to have vector point input WITH the value attached on to it. Suppose, the value of the point is the size (in hectare) of your built-up area.

then, the next question is, how to make vector point? Simple. first you have to view your land use vector layer. then, select all your built-up area including for example, stadium, school, commercial, and industrial. Use select wizard from ArcGIS/View to make your live easier. Make your selection into new layer and named it “built-up”. After you are sure you have separated the built-up area from other land uses, then now calculate the area of your built-up area polygons by using “calculate perimeter, area” from XTools ArcView.

Next step, open your ArcView and display your built-up layer. Then convert this polygon into vector point by using XTools “convert shapes into point”. Voila!!, now you already have an input for “density” functions. Go through density function in ArcGIS and choose your optimum searching area.

Any question can be posted in comment coulomn.

Thnx

Cost Distance in IDRISI

what makes cost distance more handy than in common Euclidian Distance?. See the two pictures below.

the euclidian Distance only measure direct distance from one point or object to another, regardless the morphology of the area both as a barrier or as a easiness. Best thing to explain it is with example. suppose you are in building A in the 11th floor, you friend is on the other building B on the 11th floor next to Building A with the distance of , say, 20 meters. In Euclidian Distance, it only measures the direct distance between you and your friend which is 20 meters. In reality, you have to move down , taking the stairs, elevators, or lift, walk, and take stairs in building B to meet your friend, with the total real distance, say 250 meters.

In cost distance, it calculates the friction in it process. in IDRISI Cost Distance module, first you have to have a raster point mentioning your center of object, this is the point where the distance will be measured. and the second image is the raster image of friction surface. To have friction surface, you have to convert your surface either land use or road into the friction classes.

what is friction classes? suppose i use road as a friction image. We have highway, arterial , collector, railways, and others road. How we put our new classes? suppose you want to travel as far as 100 km. If you travel in highway road, you will reach your end point in 1 hour, assuming your velocity is 100 km/hour. If you travel on arterial road, it takes 2,5 hours with velocity 40km/h. and in collector, say 3,5 hours, and others road 5 hours. ONE thing that we take it carefully is friction classes for non-road, which is in reality is the land. We can assumed as foot walking velocity which is 5km/h, so in our case, we will reach 100km after we travel for 20hours.

all this time will be our FRICTION COST. highway 1 (base cost), arterial (2,5), collector (3,5),,,,,,, bare soil (20)

we save it in AVL type of file, and run the wizards.

for my area, it was about 4 hour to run this process. I did it 3 times iteration, so,,,12 hours.

the first unit displayed in the output is in GCE unit (I forgot the abbreviation). the thing is, 5 gce means if you travel by your base situation (in highway) in certain time, you will reach 5 cells. In my case, to take 100km, it needs 6666 cells. if I assume my velocity in highway is 100km/h, this means 6666cells/60 minutes. 1000cell per minute. I use SCALAR to convert the unit of GCE into minute

happy is you can response it

pop up idea

sometimes while i’m working on my thesis, read the articles, i found a nice idea about something. today, i got an idea about ,again, how to use kriging in spatial planning.

i was reading articles from, I forgot, he write something about gis and multicriteria decision makin in vector based mode in one of the area in sao paulo brazil. it just came across into my mind that actually what he did was still taking too much time. He collected about 13 criteria to asses which municipal districts have the best quality in supporting its citizen life. But to take these 13 criteria, he has to do it manually by doing survey to random houses in one district.

so my idea is, how about if we only take smaller number of sample,,and then interpolate it,,each criterion we interpolate,, using kriging. and afterwards, we aggregate them again with their formula *overlay AND OR with some weight*

i dont think this method was used elsewhere in spatial planning. I got curiosity about this, and i try to find it in web of science,,taadraaa,,, i  didnt  get any  articles discuss about the kriging methods for interpolating social characteristics. they mainly used for *how they call it* nature phenomena such as in soil survey, forest, plant density, and recently population density.

i dont know exactly what is/are the burden of not using kriging. Or only me? yeah,,sure,i really want to know it more.

week something

i’ve done the first correction for the three first chapter of my thesis. Correction mainly on the article “the/a/an” which i rarely used, structure, flow, and grammatical of the sentences. I can say that those correction are the exact correction for me as this is the first time i write everything in english.

The last three week or so, i was struggling to correct the first chapter, I tried to know what is exactly my topic, my research question, what i’m intended to. I’m not finish it yet, but I guess it’s ok for now.

I continue to chapter two, theoretical background. while i stuck little bit at the first stage, i found out that is not so difficult to write if you focus and didn’t bear your mind with heavy things.

I also found out that IDRISI has decision maker wizard, worth to try i guess. SO, i decided to study and maybe use it, i don’t know, maybe from June as i finish *temporarily* chapter two.

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