随着国家“一带一路”倡议的推进和“新型城镇化建设”战略的实施，中西部城市群建设的步伐大大加快，坚持“集约、节能、生态”的绿色发展理念和落实“以人为本”的城市发展核心价值已经成为具有中国特色城市发展的新潮流，中国中西部大城市群的时空扩展过程及其驱动力分析已经成为热点研究课题。本研究以丝绸之路起点大城市—西安市为研究对象，利用近30年来的多时相（1985年、1990年、1995年、2000年、2005年、2010年、2015年）Landsat卫星遥感数据，提取城市化扩展过程的时空变化信息。通过引入扩展强度指数、扩展速率指数、紧凑度等定量变化指数，从时间和空间尺度上分析西安市城市化扩展的数量及几何学特征。同时，选取西安市相应的社会经济统计数据，从人口、国内生产总值（GDP）、宏观政策（包括西咸经济一体化规划）、道路交通4个方面对城区扩展的驱动力进行了综合分析。研究结果表明：（1）城市面积的变化方面：西安市城区从1985年的107.44 km²增长到2015年的724.19 km²，30年间城区面积扩展了6.74倍。扩展强度和扩展速率都呈现先降后升的趋势，在2005年—2010年达到了最大值。（2）空间特征方面：1985年至2000年西安市主要向东部、北部及西北部扩展，2000年至2015年城区则转变为主要向西部、南部与西南部扩展。（3）紧凑度方面：1985年至2000年城市紧凑度呈快速下降趋势，由紧凑型（0.367）转变为较紧凑型（0.262），2000年之后表现为缓慢下降，15年间下降了0.07。（4）城市扩展驱动因子方面：GDP和人口是城市扩展的关键因素，城区面积与GDP呈现出二次幂关系，而城区面积与人口数量则表现为线性正相关关系；此外，“西咸一体化”政策决定了西安市扩展和发展的宏观格局和规模；道路交通基础设施的配套建设也对城市发展起到牵引作用。西安市作为中国中西部“新型城镇化建设”的引领示范城市，城市发展面临着人口快速增长、水资源不足、生态环境脆弱等问题。因此，在今后的城市化发展过程中，应当秉持“绿色、生态、低碳”可持续发展理念，要加强生态功能区的规划，加快生态屏障区建设；统一渭河、泾河、灞河等主要河流的协调管理，合理配置水资源；优化产业结构，大力发展旅游等绿色产业，提高城市竞争力。

The construction pace of the Middle-West urban agglomeration has greatly accelerated with the implementation of the "One Belt One Road" initiative and the new urbanization construction strategy. Adhering to the green concept of "intensive, energy saving, ecological development" and implementing a "people-oriented view" as core value have become the new trends.
To understand the process of urban temporal-spatial growth pattern and driving forces, the urban spatial patterns at seven periods (1985, 1990, 1995, 2000, 2005, 2010, 2015) in Xi'an (the starting point of Silk Road) were extracted from multi-temporal Landsat satellite remote sensing data gathered in the past 30 years. Moreover, the quantitative and geometric characteristics of urban expansion were analyzed using the Urban Expansion Intensity Index (UEⅡ), Urban Expansion Rate Index (UERI), and Compact Degree (CD). We analyzed the driving forces of urban expansion in Xi'an city from five aspects, such as population, Gross Domestic Product (GDP), macro policy (such as the integration of Xi'an and Xianyang), and traffic conditions. These measures were analyzed using social and economic statistical data in the same period.
The results show the following. (1) Urban coverage increased from 107.44 km² to 724.19 km², which shows an expansion of 6.74 times. The annual average expansion area in the past 30 years was approximately 20.56 km². UEⅡ and UERI displayed a growth tendency after initial declines, simultaneously reaching the summit from 2005 to 2010. (2) The urban spatial pattern mainly expanded to the east, north, and northwest districts from 1985 to 2000. However, the trend moved to the west, south, and southwest areas in the next 15 years. Meanwhile, CD showed a rapid decrease of 0.367 to 0.262 from 1985 to 2000 and then slowly declined by 0.07 since 2000. (3) The urban area presented two power relations with GDP and displayed a linear positive correlation with population. Finally, government policy, such as the integration of Xi'an and Xian Yang, can influence the urban macro structure, scale of expansion and development, road traffic, and infrastructure-supporting construction.
As a Middle-West China megacity, Xi'an plays a leading role in the new urbanization construction strategy. However, urban development faces problems, such as rapid population growth, insufficient water resources, and fragile ecological environment. Therefore, we suggest that the government take the "green, ecological, low-carbon" sustainable development path, improve the planning of ecological function areas, accelerate the construction of ecological barriers, reasonably allocate water resources, and develop competitive industries.