Animated Indonesian Earthquakes Map


GIS: Flow Diagram


Today, in the GIS class, I learned how to make a flow diagram. The flow diagram can help us to see the steps and tools we do before completing our DEM (Digital Elevation Model) map using the raster calculator or the weighted sum.

You can also see the diagram to make sure there is no missing step before creating the end product, especially when you are dealing with a lot of layers and several tools that requires calculations and analysis like visibility analysis or suitability analysis (either with the boolean operations or the fuzzy membership).

If you make a mistake for a layer, you can always check again your step as well as the calculation in your flow diagram and correct it directly. To make a flow diagram, you can use the model builder in the ArcMap by right click the data in your catalog and create a new model.

Wanna see how my flow diagram looks like for the suitability analysis in GIS (scrappy paper version)? Check the video below!

GIS: LiDAR remote sensing


Belajar soal LiDAR (Light Detection and Ranging) di GIS class

Apa sih LiDAR itu?

LiDAR menurut the NEON (National Ecological Observatory Network) Scienceadalah sebuah teknologi dengan sensor laser (cahaya) jarak jauh untuk mengukur tingkat elevasi (ketinggian suatu objek dari titik tertentu) dari permukaan tanah, hutan atau bangunan dengan resolusi sangat tinggi.  

Bagaimana cara mengumpulkan data dengan LiDAR? 

Pengumpulan data bisa dilakukan di darat (meletakkan alat sensor di atas tanah), di udara (menaruh alat LiDAR ke pesawat terbang) dan di luar angkasa (menggunakan satelit). Caranya dengan melakukan semacam scanning dengan gelombang elektromagnetik seperti infra merah dan sinar hijau. Kenapa infra merah dan hijau? Karena dua gelombang ini yang paling kuat pantulannya terhadap kedalaman (perairan) dan daratan. 

Airborne LiDAR data?

Pesawat terbang melakukan scanning wilayah yang ingin dipetakan, lalu GPS (Global Positioning System) akan melacak altitude serta posisi X,Y pesawat dan mengetahui posisi benda yang discanning. Inertial Measurement Unit (IMU) akan melacak posisi kemiringan pesawat agar perhitungan elevasi bisa lebih akurat. Lalu, mengunduh semua data GPS yang terlacak dengan menggunakan laptop.

Ukur ketinggian benda atau permukaan?

Altitude pesawat (lokasi ketinggian pesawat) dikurangi dengan distance (travel time x speed of light: 2. Kenapa dibagi dua? Karena sinar dikirimkan dua kali, ke tanah dan ke atas pesawat lagi untuk ditangkap sensor LiDAR). 

Doc. Utami Diah Kusumawati/ GIS Course, UNL

Keuntungan pakai LiDAR dari Fotogamatri?

Bisa filter vegetasi jadi gak cuma scanning ujung benda, misalnya pohon, dia bisa tembus dan mengkalkulasi jarak antara batang dan daun pohon terus juga ke tanah untuk menciptakan Digital Terrain Model (DTM). Kalau fotogamatri gak bisa. 

Bisa dibuat visualisasi bermacam-macam khususnya untuk menerangkan density variation (ragam kepadatan) dari sebuah tempat ketika melakukan survei. 

Terus kaitannya sama ArcGIS 10?

Data yang dikumpulkan melalui sistem LiDAR ini (dalam bentuk LAS dataset) kemudian akan dibuat visualisasinya atau pemetaan umumnya dengan menggunakan program ArcGIS. 

Manfaat untuk jurnalis?

Sebenarnya LiDAR ini merupakan piranti yang sangat mewah, biasanya, sih, dipakai buat survei berkaitan geologi, agronomi atau juga kebencanaan. Nah, tapi data yang dihasilkan oleh LiDAR biasanya bisa diakses secara gratis oleh publik untuk dibuat visualisasinya, misalnya peta. Untuk jurnalis, tentunya ketika hendak menuliskan artikel, visualisasi yang berupa peta ini bisa digunakan untuk membantu menerangkan pola kepada pembaca atau biasanya membantu jurnalis investigasi menemukan pola tertentu.  

Untuk hasil peta lengkap yang dibuat dari data LiDAR, menyusul minggu depan, ya. Tapi, sedikit gambaran proses bisa dilihat di video berikut. 

GIS: Visibility Analysis


Map of Maya site of Copan, Honduras. Created by Utami Diah Kusumawati.


This is actually the most difficult map that I have made in the GIS class using several tools like viewshed (boolean), reclassify and visibility. Furthermore, we also had to count the percent_vis and extract value to join before getting to the final data that would be used for the visibility analysis. The map looks simple but the process of creating such a simplified and clean map is painfully challenging. This is what I called the beauty of mapping because it can simplify complex data into a pattern like above. (Meltedheart!)

I will post the steps and details about the data that we use in the class after the semester ended 😛 Magma is being erupted from my head for now. LOL.

key points: algebra map, tessellation, rumpled space, interpolation, tobler’s law (thiessen polygon), DEM (digital elevation model), viewshed, cost-surface analysis, visibility analysis.


GIS: Choropleth map


This week, I learned about the making of Choropleth map using ArcGIS in my GIS class taught by Heather-Richards Risetto. Choropleth map shows differences in regions, or in a geographical area in a form of color shading. The color shading is made to convey patterns behind complex statistical data. I love this map honestly because it’s a bit artistic with the color playing and shapes. The visualization reminds me of puzzles!

I have created this map before in my data visualization class with Matt Waite using R studio with packages like ‘devtools’, ‘sf’, ‘ggplot’, ‘colorbrewer’, and ‘dplyr’ and a small portion of coding.

Doc. Utami Diah Kusumawati
Doc. Utami Diah Kusumawati

However, in this GIS class, I don’t need to use coding commands as I only use ArcGIS to make maps by joining and inserting data to ArcGIS.

So, what steps should be considered when creating Choropleth map (joining tabular data with the spatial data)? First, you need to make sure you have two forms of files: CSV and SHP.

CSV file is like a spreadsheet of all of your statistical data, or data which contains information or numbers that you want to insert as points, lines or polygons in your map. If you have data from the government or any kind of organizations, please, please, please, ask them to send it in a form of a spreadsheet. It will be easier for you to clean the data and use it for the sake of this mapping creation.

Second, make sure you also have the shp file. Okay, what is a shp file? A shp or a shapefile is basically a vector data which has information about the attributes of a geographical area including location and shape. It usually has the longitude and latitude information as it will be the geographical template or the first layer for your statistical data. Still confused? Okay, I am gonna show you the physical forms below.

This is my CSV (tabular) data for my forest fire map. Doc:Utami Diah Kusumawati

Third, you need to have similar features or attributes to merge those two files. What kind of similar features or attributes? We merge tabular data and vector data with a field called GISJOIN or if you have latitude and longitude info in both of your data that shows the same location (or minimum having addresses will be sufficient to be merged with the vector data), it would be great. ArcGIS will automatically combine these two data (tabular and vector) into one. I remember Matt telling during the consultation session,” making a map is easy if you can find similarities among two data.”

And what are the steps to combine the data? It will be a little bit longer to explain here because you need to do several steps like intersect, join, add new field, field calculator, calculate geometry, and so on (Don’t get scared! lol).

But, I am gonna update you next week after completing my interviews and transcribing all of my interviews in Palu (since I will have a routine of doing one-on-one consultation with Matt every Monday). So, I will share with you first the end result of my lab assignment to merge data from the US Census Tract with the vector data (shp file). Here’s the final result: